I ran into this problem myself and found a remarkably easy solution:
Basically, I bought a metal junction box cover plate from Lowe's for $.92 and made it into a replacement mounting plate for the T-Stik Plus. The plate I bought measure 4.625" x 4.625" and had a perfect hole already cut into the center of it. I simply had to punch out the circle from the center and drill 8 holes into it.
I used the original metal plate from the T-Stick Plus as a template to drill the first set of holes. I lined up the center "joystick" hole with the punched-out hole of the junction box cover. This first set of holes are the screw holes which attach the plastic base of the joystick to the plate. I also counter sunk them to match the original. The metal of the junction box plate is fairly soft so it's not as difficult as it might sound.
I then lined up the center hole of the junction box plate with the base of Happs Competition and drilled the mounting holes out. You could, of course, line up the plate with the holes in a control panel and just mark them off that way. You'll have way more flexibility with the junction box plate than the original.
If this isn't clear enough, let me know and I'll post some pics. It's almost hard to believe how well a junction box cover works in place of the original plate. Well, I suppose they're both just small squares of sheet metal, but still....
