I believe one can overide the splash screen and unlock the NAV for $99 with this device:

http://www.coastaletech.com/nav_kit.htm

made for the Prius, so I would call them first and verify its use for the CamHy

They also make the interface to allow the integration of a backup camera - if anyone has the guts to try it...as much as I want it, I don't
http://www.coastaletech.com/viewtech_2005.htm

according to the website:
"A NEW LINE OF VIDEO/AUDIO INTERFACES WILL BE ANNOUNCED AND START SHIPPING JULY 18TH. THESE UNITS HAVE MANY ENHANCED FEATURES AND WILL BE COMPATIBLE WITH A LARGE SEGMENT OF TOYOTA AND LEXUS MODELS."