You can't unfortunately. Unless you decompile the game apk and edit some links it has to point to the directory of your usb drive, usually /sdcard/usb storage, but that would be like looking for a needle in a haystack. Plus you will need to re-sign the apk when recompiling. After of course you have secured a copy of the game developer's source code, which you won't get simply by begging.
You can edit voldfstab and run the tablet thinking the usb otg as /sdcard, but having that dangling thing all the time even when not using it seem a lot of hassle.
Sent from my Nexus 7 using xda app-developers app