Access for Shut-Off Valve
I decided to install an A.Y. McDonald 6001 series brass stop and waste valve (for example, on Amazon, ASIN B003MXYJOU).  Such units are much more expensive than a common valve, and I was hoping to avoid that expense. However situations like mine are just what they're designed for.
Reading other answers on the site, it is best to prioritize quality and reliability when making plumbing repairs in difficult to access locations.