Retro fitting Bluetooth in a 2005 Prius

I'm the proud owner of a 2005 Prius with no Navigation and no Bluetooth pre-installed.

I plan to mount a Sony Ericson HCB 700 Bluetooth controller for my cellphone.
The display unit will have to go on the dashboard, just beside the MFD, but I've not yet decided on where to put the control knob.
I was thinking of putting it on a mounting bracket on the flat surface just below the glove compartment under the radio unit.
Now, before I start drilling the hole, ... does anyone know if there is anything sensitive behind that panel ? Any reason this might not be a good spot?
I'd need to mount a 2x2" plate solidly enough to resist some pushing and turning in the operation of the control knob

For refernece, the HCB 700 unit is described here:
http://www.allmobileaccessories.co.uk/buy/...n-hcb-700.shtml

Thanks for a really nice site !