After a lot of searching around on the web and also talking to other birders, the LCE Adapter from the London Camera Exchange seemed the best bet. This is a very simple, bucket shaped, anodised aluminium device which screws onto the thread mount of the camera lens and then slips over the telecope eyepiece - although it still costs £50! It comes with three thumbscrews to secure it in position, but I found these very fiddly and inconvenient.
Following a tip I found on another web site, I have wrapped PVC insulating tape round the knurled zoom-grip of the eyepiece until it is padded out to the same diameter as the rubber eye-cup. The adapter now fits on quite firmly and snuggly without needing any further securing and I find that, using this set up, the camera is correctly centred on the eyepice without any need to fiddle around with mounting screws.
I also use an Eagle Eye LCD sunshade and cable-release arm which I already had for using the camera with my binocular microscope. So when I am out digiscoping, I have the LCE Adapter and the LCD shade/shutter release arm already fitted on the camera. I carry this whole assembly in a belt pouch. When I have the 'scope trained on a subject I want to try and photograph, I just lock off the pan and tilt on the tripod head, lift the pre-assembled camera out of the belt pouch and slip the LCE adapter over the eyepiece. I try to remember to turn the camera on as I get it out of the belt pouch so, by the time it is in place on the eyepiece, it is all fired up and ready to shoot and, hopefully, already lined up on the target. When I have taken the shots I want, I just lift the whole thing off the eyepiece and put it back in the belt pouch. Smple and quick!
This seems to work for me. The main problem is getting the thing onto the telescope's eyepice without disturbing the positioning of the 'scope. If the 'scope does get moved during the process, then finding the target again through the camera viewfinder can be a challenge!
