Apartment leasing question, wont' allow a third friend to lease with us.?

My girlfriend and I are looking at a 1008 sq. ft. townhouse for 765 a month. It's a two bedroom with 1.5 bath condo with a nice living room and all. Now we were hoping the management office would allow all 3 of us to sign a lease together but they won't do it, they only allow 2. So we were thinking and i can't find a single thing on the internet about this but could my gf and i sign the lease and have him crash there while paying his share of the rent to us so then we can pay our landlords? He's been a close friend since 2 grade and i know he'll never bail out on me so that's not a worry. Can we get in trouble for having him there without them knowing he's paying a share of the rent to us? Do alot of people have this situation? Will it get us in trouble? anyone done this before? i need help cause we really want to get this place.