Obviously sending yourself requests from another account to your main account is the easiest solution. A silver x-box account will suffice.
Make sure the settings are as follows:
Challenge Terms: Highest Score
Number of Tries: 1
Friend: Select your main account that you wish to obtain this acheivement on OBVIOUSLY.
The rest of the settings don't really matter as long as you make sure you only have 1 try set.
Games I find easiest are ones that you can fail on fairly quickly such as Crystal Castles.
If you have the game set to highest points then simply run into the enemies until you're completely down and out on your side account then on your main account beat the challenge set!
Obviously there are plenty of games you can kill yourself on swiftly...(LOL)
Send 20 challenges with your side account and beat them all with your main account and you're done here!