As I live in the land of bikes ( Holland) I suppose I should be able to assist.
Their are two good mounts specifically for bikes that I know of
1) Arkon
http://www.arkon.com/pdamount.html
This is a universal mount. My only concern is how secure the side grips would be. Personally, I would use the bike fitting and replace the holder with a specific one for the PDA. OR look for a ruggidized case for the PDA.
2) Richter . This is cheaper bike fitting that is designed to fit PDA specific holders
