Hi silv,
I would just be attaching a ball joint tripod head to that top plate that is already there. It looks like there is already a thread there to do so, but if you don't find this "beefier" enough or not the right size for the thread on the bottom of the ball head, then I would drill a new hole in the middle of that plate and put a bolt through it. A ball head allows you to point the camera where ever you want in the sky regardless of where the telescope is pointing at the time for piggyback photography. As long as you are polar aligned, with an equatorial mount your telescope could be pointing east and your camera pointing straight up for example and it won't make any difference.
I'll attach a pick of the ball head setup I use if you just want to run a camera on the mount without the telescope.
Out of curiosity- are you on DeviantArt??? (forgive me if I'm wrong)
Cheers
Greg