The stock gauge has a light, so there's power there for the gauge light. If you're using a mechanical boost gauge, that's all there really is to power up. I don't know what kind of cutting and hacking is involved with putting the gauge itself in there though. I'm about to find out... I'm going to pull my cluster soon to see if mounting my Apexi mechanical boost gauge in there is a viable project. I hate bulbous gauge pods ejecting from my dashboard blocking my view... and pillar pods cause the gauge lights to be annoying at night. Especially with EL gauges. Plus it puts the gauge right above the AFC Neo that's in the slot where the ashtray used to sit.
When I get to doing this part of the car, I'll post what I find.
Oh also, since the stock gauge is an electric gauge, the pressure signal is there from the stock pressure sensor, so if you buy an electronic gauge that uses an identical type of signal you should be able to wire it right up to the stock sensor, or at least use the stock wiring to connect the aftermarket sensor to under the hood. As to what kind of signal the stock sensor puts out... you'd have to test it with a DVOM at known pressures or see if toyota printed up sensor test info anywhere and compare it to the sensor on the guage you want to use.