We have (had) a member, Dagwood, who advocated soft mounting and to date is the only one who has done something that should have worked. Unfortunately the man hasn't posted here for a couple of years. (No jokes about crashes, please)
Here's a link to an old thread with some very good reading and photos of his concept. http://motorbicycling.com/showthread...600#post347600
Keep in mind, this information is not meant for a first time builder or those without metal fabrication skills and/or the tools to do it right. It's just for discussion.
If I understand him right, this is a concept that Boxcar was talking about earlier when he said, "Picture a shock absorber mount".