Hypothetically, you could change the name of the models and materials to be that of the m249. Wait a sec while I find the right name.
Okay. Just change rif_m4a1 to mach_m249para
Just like renaming any other file, but make sure the w_ and v_ are still there.
Ignore rif_m4a1_sil. Just delete it.
I've done this before for going from the sig550 to the AWP, and it worked just fine.