Instead of giving the players an iterative attack every time theyre BAB reaches a multiple of five, give it to them whenever they reach their weapon's max damage.
Daggers (1d4)
+20/+16/+12/+8/+4
Sword, Short (1d6)
+20/+14/+8/+2
Hammer, Friggin Huge (1d12)
+20/+8
Etc.
Thats what Ive been doing and it works perfectly for my campaign. It even works for firearms, as a higher caliber gun would have more recoil.