Hi Peter,
I am trying to do the same but am baulking at a QHY5 with a guide scope. When I tried to use my 5" reflector mounted piggyback on the 8" reflector, the drive made some bad noises as the set up was too heavy for the gears at full horizontal extension (tube and counterweights horizontal) so I decided to ditch the guidescope idea and keep as light as possible on the HEQ5 pro.
I have successfully mounted my toucam onto the 50mm finder (dodgily) by removing the cross hair bit at the back and mounting the toucam to the back of the finder. (read double sided tape and elastic band) This is just proof of concept at the moment, I will mount this properly if I can get good guide star exposure and find them easily....
My plan is to run both the Canon 1000D and the toucam guiding via Maxim DL5 which can handle both cams and guide through the Eqmod pulse guiding interface, so there is no need to use a GPUSB to convert back to ST4 compatible instructions on the guide port.
I have yet to test this set up, but it is all assembled and waiting for a clear (and COOOL!) night for me to give it a burl.
Fingers crossed it works, I have tested the camera through the finder terrestrially to check focus so this seems to be fine, just need to do it in the dark.
Of course, if the toucam is an issue with the exposure etc, I am always keeping my eye out for a QHY5 on the IIS classifieds to use this as a finder guider...hoping I can use what I have got for now.
Also, why not check out a Long Perng 66 ED carbon fibre tube for guiding ($399 at Andrews) as I have my eye on this one if I need a dedicated guidescope later on... $399 is a bargain for a CF tube ED!!! Just need to wait for Pay day and see if I can slide it past the missus. Check it out
here
Good luck
Cheers
Chris