I've been looking at all sorts of possible ways to mount my cell phone in my car... I cut sheet metal. I used gutter guard (leftover from protecting my intercooler). Finally, I got a dumb idea.... I found an L-shaped mounting bracket. The long side was about 6" and the short side was about 2". I had bought a cheap 10USD cell phone mount from WallyWorld. I mounted that to the short end, and slid the other end into the gap between the air vents, and the head unit. The L-bracket was about 2mm thick. Sturdy as a rock, and I can slide it back and forth. May not be the BEST method, but it worked out well for me

Another angle to give you an idea of how I mounted it to my phone mobob.

Final shot! This is what it looks like when mounted all the way in. Pretty slick, if I say so myself. The space goes back about 4-5". Because the L-bracket was longer than that, I've got plenty of room to push buttons behind it.