Just enable friendly fire.
For the most part it won't be a huge deal. It'll solve the 15 v 1's that we see all the damned time.
If I have to check *my* fire because some idiot dives in front of my guns because *I'll* get hurt, that's just BS.
Of course assign a penalty. Maybe Perk points and a warning. If you frag 2 (within say 12-24 hours), your score for the tour get's zeroed and your grounded in that country for 24 hours (this'll take care of any score potatos who take out friendlies to get the kill their countrymen worked so hard for).