You need to short circuit the mobo cable by connecting the green wire on the 20 or 24 ATX power connector to any one of the black wires on the same connector which will force the PSU on. A paperclip bent to fit usually works well for this.
As for modding idea how about a green "energy saving pc" hooked up to a wind turbine which is easy to build always wanted to try that. Also one that has a minature diesel engine in that runs off mineral oil (also submerge all components to make it a case coolant and fuel tank
). Then convert the kinetic energy of the diesel engine into electronic power and make the unit self contained. Could also place a touchscreen on the side panel to make the unit completely wireless :P just a single box which magically powers itself it would also be near silent providing the proper acoustic dampening rubber mounts were used. I think that would be a ground breaking mod.