I know some very highly reputable people who use 20 pin power supplies in DFI nF4 boards, and they work fine. As I say, I recommend
using a 24 pin PSU whenever possible, but if you can't, you can still get by on a 20 pin PSU.
jumper mod was made specifically for relieving BH-5s users of the 5v rail load who are using 20 pin power supplies. I know that every one on dfi-street will say the opposite, but there are a lot of people over there who are quite full of themselves and believe that a fan qualifies as passive cooling.