Currently im thinking of taking the following steps:
1. Add on some very thick foam handlebar grips, with some weatherproof but removable glue.
That won't fix the cause of the vibration..just a band aid.
2. Add thin rubber under the flat handlebar mount bracket and the seat post mount all the way along the inner tube (if it will fit!).
Same as above.
3. True up the motor alignment, add another set of rubbers (2x) to the engine mounts and tighten all mounting bolts
If you feel the motor has shifted you can make a "L" bracket to stop this from hapening..look at my photos. http://www.motoredbikes.com/album.php?albumid=892&pictureid=5578
4. Give the clutch and chain a really good greasing/oiling.
Doubt that is the cause but won't hurt.
5. Mix some fresh fuel with a racing 2 stroke oil (currently inadvertently using a lawn mower 2stroke). (Will this/Could this have an effect on vibrations?)
I really don't think so. I have never experienced it in any 2 cycle.
6. Grease and repack wheel bearings, retighten, check tyre rim for buckles and attempt to fix as possible, check tyre is not out of round.
Possibility.
Any other happy time generating vibe tips appreciated!