I also have GF1 but never considered anything bigger than an manual 50. Since you have a G1, you maybe able to do much better because you can stabilize the lens and camera in the traditional SLR way, where as a GF1 without a EVF adapter is not going to be a good platform for a long lens.
But I have heard of others using the EP1 on this forum which have had success with tele.
Good luck
Edit - since your question pertains to having no image stabilization
Forgot to mention that before image stabilization - to get good picture w/o tripod
1. good stable stance
2. three point camera hold with one hand on camera body, one on lens, your cheek against the body of camera
3. shutter speed 1/FL min. needed (FL for focal length) --> modified for m43 --> 1/(2XFL)