Not knowing the type of paint makes a difference.
First off he should make a claim with his insurance. Then he could try a few things without worrying about screwing his paint. I have dealt with cars that people have painted spots with a paint brush before and i used lacquer thinner. The LT will soften paint quickly and he might have to polish it after it sets up again, as it could cloud the paint.
I think he should try a spot with LT- only on the problem paint, and this would give him a starting point. If it works then try to keep the LT off the cars paint as much as possible for the longest time. At the end of this work he will have to allow it on the cars paint, just don't let it dwell for too long.
If this process works, he might have to do it over a couple of days, and let the cars paint harden.
It could also be wetsanded off but this would be alot more time and professional.