It's possible, but you'll need to recreate the preamp circuitry of the head. Do a google search for RM100 circuit diagram and it'll give you an idea of what you need to build.
Emperor-TK did an awesome job on his bass head - http://mtsforum.grailtone.com/viewtopic.php?t=20732
It'll give you some idea of what's involved - basically almost everything Emperor-TK did but without the output amp.