But thats not so difficult then ? You can take one of the switches of the transmitter you dont use off, and insert/connect a cable through the hole towards an old joystick.
See my profile for a picture of the transmitter as we used for our old heavy Project 2: Hexem.
In our case we didnt damage our transmitter at all, we used an existing hole and made a connection that was provided for by the manufacturer. (You can see that between the 2 switches above the sticks there is a 3rd hole ready for extra switches, we simply used one of them...)