hmmm, i would do it with a little shader...for a little model-seperated from the gun, it shouldn'T be too hard, this way:
you give 2 bmaps to the shader, one times a texture and one time a pic with numbers from 0-9.
in the pixelshader you have to chaeck the x position ad compare it wiht agiven one, to see which "part" is rendered and put the numbers there...
Hmm, i should give it a try