Linux yum through a socks v5 proxy

nylon supports SOCKS mirroring with ACL's

http://monkey.org/~marius/pages/?page=nylon

An alternative would be to do is to do something like:

ssh -L 3000:10.0.0.5:3000 -L 3001:10.0.0.5:3001 .... -L 4000:10.0.0.5:4000 12.0.0.10

This will set up a thousand and one seperate ssh tunnels for each port. I have never tried setting up over a thousand simultaneous ssh tunnels, so I have no idea what the performance is going to be like, or if it's even going to work at all, or if you're going to have to set up multiple parallell ssh processes.

It's going to be a pretty long command line, I would suggest writing some kind of script to actually invoke the command.

All in all I would not recommend this, if at all possible, set up a VPN.

Is there any reason your users can't just connect to 12.0.0.10 directly? Or are the ports not exposed through the firewall? If not, can't you just open up the ports in the firewall from selected IP addresses, or do you have security considerations that don't let you do this?