Re: SG tone in a strat?
I'm assuming that your friend's SG is a mahogany body with a set mahogany neck and rosewood fretboard. Also, unless he's upgraded his pickups, then their probably lower output Alnico's.
So, your talking about one of the warmest setups a guitar could have with your friend's SG, then your Strat, even with a rosewood fretboard, has a trem, which thins out the sound, Poplar body, also a brighter sound, and a bolt on neck as well. With single coil pickups, these two guitars are really opposites.
You're going to need a humbucker in the bridge of your Strat to even come close to warming up the sound. I'd also suggest blocking your trem. Get a APH-1 Alnico II pro, or Custom Custom.
Honestly, my suggestion would be to keep your Strat in its configuration, save some money (Christmas is right around the corner) and look for a used Epiphone SG in a similar configuration to your friend's. Then you'll have a couple of guitars with a wide variety of sounds. Most guys who want a wide variety of tones probably have one Strat and one Les Paul or SG type of guitar.