Hi Gordon - welcome to Surfbirds!
Are you talking about a set-up that you could take into the field? One that you could quickly set up in a hide?
I'm sure people would have many suggestions, but my first thought was to pirate one of those 'nest-box cam' kits. The camera itself is weather proofed and they are designed to be laptop compatible. Whether this could be patched into a digiscope setup, and also whether it would give an acceptable image is debatable...
Are there no small video cameras that would serve the purpose?
You might get more sensible advice from Bo Boelens (the Fat Birder), either through the Fat Birder website or through another site he set up which is
This was formerly the Disabled Birders Association. Bo is a great bloke and very approachable - he may have a ready-made solution to your problem or at least be able to point you in the right direction!