I've following situation

there is huge LAN in our university where i have got root permissions on a subnet router (subnet, The LAN is connected to Internet via NAT (all local ip's are tranlsated to one inet) and only ports 22,23,25,110 are open from local machines.
I have no permissions to deal with main gateway ( bsu.by ) , but often need to connect to my from Internet. Is there any possibility to make such a 'reverse' channel?
It would be great to make something like VPN connection from a remote host to join my subnetwork, but just ssh connection would be enogh good.

Another trouble is that my ISP gives me a different IP for my remote host every time i dial up