The piping is different lengths between the GSR and the LS. You might be able to modify it, but it would probably be a little difficult.

However, an LS 2-door and 4-door exhaust are the same except for the size of the exhaust tip coming off the back of the muffler. If you don't mind your tip being tucked up kind of underneath the bumper, a 2-door LS exhaust will fit fine. You could probably also get a shop to extend the exhaust tip from the muffler back pretty easy. The Type-R exhaust also fits the LS fine.

I think that the A'pexi World Sport exhaust comes in 2- and 4-door sizes.