Let's say I have a small captive group of more savvy users--just the site admins, for instance. Are any of these approaches worth looking into for them?
ssh -L1234:localhost:80 adminhost.yourdomain.com
then hit http://localhost:1234/ in your browser to reach port 80 on adminhost.yourdomain.com.
Simple and clear. The user isn't accidentally going to do their personal browsing over the admin network.
Make sure that the server on adminhost is only listening on localhost (and/or that port 80 is firewalled off to the outside world)
This is what I do everywhere I need to trust a http interface.
I even make customers do it some places (e.g. if they have access to VNC for KVM guests) but it does require a certain caliber of user.