If you have a usb stick that is at least 1gb formatted in your xbox 360 to work like a memory card you could always just download the latest roster from the internet. From here for instance. http://www.megaupload.com/?d=3CFG7VU4
When I did it in the past. I would use two programs you can find in a google search. "Modio" to edit the save file you downloaded from above to edit the profile/device ID on it. And to rehash and resign so that it works. And the 2nd program is "xtaf V44" to inject the downloaded save into your USB stick.
If you do this you would first need to copy a NBA 2k12 save file to your USB from your xbox the default roster save that you already have on your xbox should work just fine. This step is so that the correct folder is created on your USB so that you know where to put the new roster file and to get your profile ID and device ID. You put that usb stick in your PC you extract your save with xtaf open that in modio to get your profile and device ID's which you will edit into to the new roster save you downloaded (Roster1.ROS). Open the new roster in modio enter your id's from your old roster and click "rehash and resign" and you are done editing the roster. Then go back to xtaf and inject the new save file in to the exact folder where your old NBA 2k11 save was on the USB. Put it into your 360 and load the save and you have the latest Roster update without XBL.
You may not even need the 2nd program "xtaf" now since modio I believe also can do xtaf's job in the new versions using the "explore device" option. However I havent used the new "Modio" much so not familiar that much with it. When I did this a while back I needed xtaf so thats how I explained it here.