Although it probably would be best to keep the rods within the tube, I don't see it as "set in concrete". I have an Xtreme (relatively new so I have not started mod'ing it yet) and, depending on the weight (which I can't find anywhere for the flexible pushrod systems I see on Tower Hobbies), I was wondering if you could just drill a few holes toward the back where the boom exits the main body, you could have the rods and their sheaths exit there and attach them (something light like pull-ties or light clamps) to the boom and lead back that way.
The boom itself is pretty thick, so those flex rods might even fit within the boom itself, but if attaching to the outside of the boom keeps them a little straighter, it might be the better way.
Anybody else think outside of the boom is feasible without screwing up the weight too much ?