Maybe it's already enough to use the window-less version of PuTTY, plink.exe? Usually, LWP::UserAgent will pick up the proxies from the environment after a call to ->env_proxy. But it seems to me you're only doing port forwarding, so real proxies don't come into play, unless you have a HTTP proxy program running on the target machine where you ssh to.

At least the two major ssh implementations, PuTTY and OpenSSH, have port forwarding, but simple port forwarding won't let you make outbound connections on the remote machine.