Thank you, it is. I need to think some more about this, but as there is nothing other than a coupler between the D-shaft and the telescope shaft, our choices are limited. Some kind of electromagnetic clutch (perhaps even something you fabricate yourself) is still on the table.
Bearing in mind you will be laying hands on the telescope to manually focus it, would it be feasible to have a manually operated clutch - something that you can slide in and out of engagement, so to speak?