what you've gotta do is
recover their GT on your box
then go to the website, click transfer licence, keep clicking next till you get DC from XBL on your console, then sign back into XBL on the console, then once again click next on the website
it should say "transfer complete, click done to auto start DL" or something like that
don't click done.. just exit it.
then go to your console, whilst signed in on their account and go to download history, then DL the maps and then Delete the GT from your box.. you can now play on your profile
I DO NOT RECOMMEND DOING THIS WITH SOMEONE YOU DON'T KNOW AS THEY CAN FUCK YOU OVER AND TAKE EVERYTHING YOU"VE DOWNLOADED, SOME OF IT YOU WILL NO LONGER BE ABLE TO USE