Can I simulate a ground electronically?

Sometime I have to test telephone lines that are ground start. In order to pull a dialtone off of these I have to ground one side (tip or ring both work). Sometimes finding a ground is not all that easy (ok most of the time it is but sometimes I just can’t get one). Is there a way I could make a ground simulator - some electrical gagit that I could touch to the line to get a dialtone w/o having an earth ground?