I don't know if this will help but there may be different ways of looking at handling tools.
(Just don't look at the prices.. you'll be thinking in terms of adapting stuff to similar function or buying cheap ebay quality)
For instance with orthopaedic surgey on small bones/patients I would use an assortment of fragment holding clamps and sometimes tiny neurosurgery power tools rather than running out of hands. Screws are kept preloaded in cassettes and picked out using sprung sleeved screwdrivers.**LINK**
**LINK**
Power tools like die grinders that are activated by clenching the palm over a long flat lever rather than single finger controlled.
Gillies needle holders for instance are held with thumb in one handle loop and the other handle supported by first two fingers and the third in that handle loop. It gives much more control.
Assorted example bone holding forceps..**LINK**
Some will have a coarse screw thread to hold the clamping force. Those that use ratchets can usually be released by pushing sideways on the ratchet.. an action that uses the palm and a few fingers rather than a scissor-holding 1-finger-each-side action.
You may be able so set something up over a bench to use a dremel like flexible drive extension and foot speed control for driving tiny fixings.
If you consider the watchmakers tiny screwdrivers designed to be held down with one finger and twirled on the shaft then similarly one can adapt to hold larger tools down with the palm of left hand and some ratchet device gripping the shaft or a through bar