I used a brodit vent mount to fit my Desion Ice Link. Fits very well and mounts securely, although is still easy to remove if need be. Have seen a report in my local rag that theives are now breaking into cars when they see a sat-nav mount, on the assumption that the owner has simply stashed it in the glove box. If ever I'm leaving the car somewhere even remotely dodgy I remove the brodit clip and tuck it up under the dash.
The good thing about the B5 is that we have the three vents. The one on the drivers side can be closed independantly, so that you still have two open vents to let the air out of to keep you and the missus warm!