this worked for a garmin, didn't take too long and is fairly simple to do. should work with other models as well.
1. bit of stainless about 13-14cm long, 4cm wide, 2-3mm thick. mount satnav bracket on this in the middle.
2. tear the rubber from a mouse mat, cut so it fits and glue it on. i did this twice as a mouse mat isn't that thick.
3. drill a hole at each end so a bolt can go through the gaps in the yokes.
4. 2 more bits of stainless, each 6cm long, 2.5cm wide, 2-3mm thick.
5. glue one layer of mousemat on each (no clearance otherwise).
6. hold the big bit on top of the yokes and a small bit underneath. get your bolt, dip it in paint or somthing and drop it through the hole so it marks the small bit on the rubber. drill your hole here, same for the other side.
7. bolt it together, i used 6mm bolts/holes.
it's quite sturdy and the only thing touching the bike is rubber. easy to whip off as well.
http://img239.imageshack.us/img239/5679/garmin0bs.jpg