As an alternative to doing this against the AI, you can also boost this very quickly with one other person.
Set up a private match on a 2v2 map, I suggest Corvana Chasm. Invite your friend, and make sure you choose two spots that are close to each other on the map (for Corvana Chasm, choose A and C). Don't use any AIs, and choose whatever faction you wish, no Rush timer, and Assassination mode.
Start the game. Select both your Engineers and have them Guard your ACU. Start moving your ACU and have your friend move his ACU so you meet in the middle of your bases. Hit LB and select any helpful ACU upgrades that you can.
Now just attack your friend's ACU. With your Engineers supporting you, you shouldn't even lose any health.
This will also get you the Luddite achievement if you don't have it.