I bought my grandson what I thought was a cool kit...a Makedo T-Rex that was on a good sale. If you haven't seen the Makedo products, they consist of pre-printed and cut cardboard pieces and plastic screws that hold them together. Assembly is easy as you proceed attaching all items tagged in a numerical order. Up to three pieces are attached with the back one being smaller so the screw bites in. The result is about 18" tall. My grandson loved building stuff but for some reason showed no interest. So, I finally built it myself.
The T-Red has been staring at me ever since and I swear I hear it saying is saying, "Fly me." Those legs and the tail look like fins to me. I haven't quite decided to potentially sacrifice it. I'm thinking I should be sure the grandson won't miss it. Even then, the goal would be to make no permanent mods to the T-rex other than a hole in the head for the launch rod.
My thoughts are to remove the bottom structure and install a tube with motor mount installed. Ejection would be out of it's mouth so I'd need to fab a bend in said tube. A cap would be fashioned to plug the tube. I'd make card board pieces that would be glued to the motor tube and screwed into the existing structure with the Makedo screws. Thus, the guts could be removed and the original base reattached. This, of course, assumes it survives and is partly why I don't want to muck with his T-Rex.
The thrust angle and motor choice would be very tricky!