As a network guy more than a windows-dito I cannot tell you if you can share a mapped drive. However, that is not a very beautiful solution since all traffic then needs to go thru that machine. Also there must be a reason for only allowing one host thru that tunnel and my first feeling is that your request violates some kind of decision made when they built that tunnel.
The right way to solve this is (in my humble opinion) to make that tunnel transfer traffic between all hosts where there is a need to communicate so that each machine has its own mapped drive to that server.
Br Jimmy
