Where did you buy the clip? (Have a link?) I looking to do something similar and walked around my hardware store looking for a simple solution for to hold it in place.
The clip that holds it in at top is a peice of metal that I bent in to an L shape then used rubber to cover it, the rubber extends past the back end in to the dash to create a "hinge". I'm actually going to get rif of the top bracket as soon as I get the 3g and silicone sleeve in favor for a cleaner idea.
The bottom peice you see extending just past the ipod plug is basically a U shape with little wings at the top to hold the plug from dropping down when I put the iPad on it.
Picked up the 3G and put navigon on it (had it on my iPhone too) and it workin' great alng with pandora and a few other apps I've got everything I need for in car use.