Sprint LJ7 is 4.1.1. at your own risk.
Start with MG2 virgin not sure with other virgin roms...
do nandroid backup
flash sprint LJ7
##DATA#
enter six zeroes when promped for MSL.
in ADB getprop ril.MSL
nandroid restore MG2
watch out for what you flash - don't flash bootloaders, aboot, tz etc...only system, data, boot, (recovery seems safe too but then have to use odin to get orig. recovery back).
I've flashed sprint LJ7 modem back and forth from virgin M2 modem without noticing any problems. Can't remember if that was needed for the getprop thing to work. Or maybe that's the only thing needed.