How confident are you with electronics?
There are a number of sites which describe how to convert an ATX PSU to a Lab Bench Power Supply etc which include instructions on overcoming the sense voltage issue (if the PSU doesn't detect enough draw on a 5V line, it won't turn on) but none seem to be straightforward.
I did some googling hoping that there would be a simple 'cross wires X and Y' or similar; some of the solutions might make sense to you, or someone else on the forum might be able to give some more advice.
