Extending network over a dry pair

A quick question for you guys; If you had a single dry pair (pair of copper wires originally for phones) to a remote site that was around 6 miles away, what would you use? We currently are just extending a T1 line to this site, but 1.5Mbps isn't cutting it anymore. Unfortunately it's a research site on a federally protected wildlife preserve so we can't run any new infrastructure (fiber etc) and it isn't in a geographical place where point to point wireless is practical. We were thinking there is some sort of network extender that uses some form of DSL for higher bandwidth capacity. Any suggestions?