Ok, my other solution took too long compared to the Release method, so I've removed it.
Instead, I'll spell out how to do the Release method. You should be playing in the Keep Away 1v1 playlist, however, this will require you (and your partner) to have the Strategic Options DLC. Also, you should only do this during times that Keep Away 1v1 shows as 'Low Population' to reduce the chance of getting someone else. And make sure that you and your partner Prefer each other.
The player going for General should be the Prophet of Regret. I've tried it with the Brute Chieftain and there was less room for error with him.
Start off with the following build order...
Send your Ghost Scout around collecting supplies, but being careful to avoid the Flood bases. You don't want to lose him as it may impact your final bonus multiplier. Once the Temple is built, the Prophet will be available. Send him to the three Flood bases and the two releasing mechanisms. Keep him out of reach of the tentacles.
As soon as you have the cash, upgrade him to Blessed Immolation. This will make taking out the Flood bases quicker. Once they are gone, send the Scout (or the Prophet) in to take the supplies. I generally send the Scout as I can have the Prophet moving in the mean time.
Upgrade your Warehouses to Blessed Warehouses and upgrade to Citadel ASAP. Build a Training Hall and a Summit. Research Peons and the repair thing for the Engineers. Build 2 Jackal squads, 5 Grunt squads (or ignore the Jackals and make 7 Grunts), and 2 Engineers. Upgrade your tech level when you can. Research Harmonious Digestion, Needlers, and Deacon. Once you've gotten those squads and techs researched, recycle those two buildings. Build 2 more Warehouses and upgrade them when you can. Research Followers, Ancestral Perversion, Divine Absolution, and Shield of the Forerunners when you have your Tech level maxed.
As your Prophet cleans out the releasing mechanisms, hot drop a single Jackal (or Grunt) squad to him and garrison them in the mechanism. Repeat for the other when you get to it.
After all Flood bases have been destroyed, move your Prophet to one of the release chutes. Move the other 5 Grunt squads and the Engineers to the other.
Wait for your cash reserves to build up and then build a Scarab. While the Scarab is being constructed, wait for the reserves to fill back up. By the time it is finished, you should have close to 3k. Move the one Scarab to either the Prophet or the Grunts. When the second is finished, move it to the side that the other one didn't go to. Make sure that the Scarabs are not too close to the chutes. Give them some room so their beams can swivel rather than forcing them to turn their entire body.
At this point, you should be at about 18-20 minutes, give or take. I did this without making another base.
Now, you can start in releasing the Flood units. The initial release costs 300 cash per side. Recharge time for that is 1 minute (or so). Second release is 600 per side. Recharge time after that one is 2 minutes, iirc. Third release is 900 per side. Recharge remains 2 minutes. You can check how much time has elapsed by hitting the < button by the Guide button.
Now, you might be asking why include the Grunts? Well, it's because they are very very useful at taking out the flying Flood forms. If you do this right, you won't lose a single unit. The Engineers keep the Grunts healed, and the Prophet's shield will not collapse under the Flood assault. The Scarabs are tough enough that they won't lose more than about 1/8th of their life.
Once you have your 4000 points, send the nearest Scarab over to the other guy's base and have it destroy it.
It will take a grand total of about 50 minutes to complete one iteration of this method. At the end, if you haven't lost anything, you'll get an 8.4x bonus, meaning the full 33,600 points for the one going for General. I'm trying to do about 4-5 matches a day. At that rate, it'll take 6 days or so to get it done. You'll need 29 matches, if you are starting at 0 points.
Edit - Don't worry if you lose a couple of Grunt squads to the Flood. You shouldn't, but it occassionally happens. They should be arranged closely together in an arc a little bit from the release point. Close enough that they can fire their needlers without moving, but far enough to give them a bit of a breather before the ground troops get to them. I think in the 20 or so runs I've done so far, I've lost less than 10 squads.
You may also notice that in the final stats that you can get a lot of squads 'lost'. I believe the system counts a single infected grunt as a whole unit. These don't count against you in the final multiplier.