Using 2 PSU's is fairly safe. I have run 2 in all my rigs in an always on setting, crossed the switch cables(green/black). I did this for about 8 months until I bought a pin removal tool and spliced the two together. I always worry about fire, not because of the PSU necessarily but because it's very hot, always on and it draws a ton of power.
I just use a paper clip, or other little piece of metal to stick into the green/black pins in the middle of the plug. (there are pics online about this)