I have posted the issue out to the community and received some great ideas; a kiosk extension may be what works in the end to remove the right-click copy issue, but it will take a fair bit of my brain to figure that out, or cash for someone else.
I did discover that adding ?rm=minimal at the end of any gdoc makes the menu disappear, producing a blank canvas for docs and drawings; cool. What other sneaky tricks are out there? How do we find out about them other than by searching for hours in stackoverflow?
For now, I've settled on a combination of doctopus, ?rm=minimal, awesome table gadget with the proxy script, and sites to show each student their own doc when the edit access to the doc is set to anyone at school with the link can edit. The students can still right click copy but this is fine according to the assessing teachers; they couldn't stop the ability to copy in a .doc but now they don't have the menu to tempt them 😜