After seeing this guys vid's, looks like cap technology has came along way.

I would assume all i would need is a big enough cap and a voltage regulator for 4.5v or maybe skip that just power it right from the +5v rail.

but i might need to isolate the cap from the 5v rail once the computer is off.

next what size cap to choose, how many UF or F's?

check out this video where this guy gets rid of this car battery and just uses caps to start / run his car every day.

holy moli 350 F!