Filter all outlook traffic on network via a single OpenVPN Client?

Hi all, my first post on the forums so I apologise if I have placed it in the wrong section.

My current situation is I wish to set-up all our IT Suite Computers to allow staff to login to their outlook for our head office/Company Emails. now our head office uses OpenVPN to allow external connections to their Win2k3 exchange server which uses Active Directory to authenticate. Now my actual question is it possible to filter all Exchange traffic from outlook clients to a Single OpenVPN type client from the external network we have setup on this site? sort of like a proxy as I've though of this idea before just don't know if it will be configurable/Is possible. At the moment in time we have to have OpenVPN installed on every Client PC that we need to connect to the head office Exchange server I want to change this so we have a single client that authenticates to OpenVPN server then allows us to access the exchange if this makes sense.

If it doesn't please let me know so I can try and explain it either via diagram or in another way that may be understood.

Thanks.