Does it have boles in the tubes for which to run the casing? My old MTB from days gone by required the cable casing to run through the tube. You could always go singlespeed

If that's not your style, I suppose one solid length of cable casing would do it. Does it at least have cable bosses where the FD and RD would go? If it doesn't, good luck getting it to work without brazing something on to hold the ends in place.