I built one of these models a while ago just for fun, but I think it might be possible to convert it to rocket! http://www.navy.forces.gc.ca/cms/5/5-a_eng.asp?id=608 (The model is at the bottom of the page.)
I'm thinking the motor tube could be mounted in the back of the ship with some custom square-ish centering rings, and and have an inner tube running the length of the ship, where the parachute would be packed. I'm thinking the front couple inches of the ship could separate as the nose cone. Fins could be attached to the sides and bottom of the ship, and one on the top of the motor tube. I'll definitely try, and I'll let you guys know how it turns out!
Here's a pic: