Using 2 modems

I have a MS Proxy Server with 80 users. This proxy server is used only to connect to a remote RAS server that has multiply modems by just the 1 modem in our Proxy Server. Once connected, the remote site has a web server that we connect to and we do our business. When just one or two users are connected it’s not that bad, but you can imagine if 3, 4, 8 or more are connected it comes to a crawl. The Proxy is set up to do call on demand. Is there a way to put another modem in our Proxy that calls the remote RAS server so we have twice the speed between locations?
Thanks