rear parking assist

Does anyone know what it takes to add the rear parking assist feature? My wife has backed into yet another post and this time put a good size hole in hte bumper molding I'm just wondering if all the wiring is there and it just needs the sensors?
I found the replacement part and they list with our without the sensors
http://www.trademotion.com/partlocator/index.cfm?action=getLocator&siteid=721&chapter=DR1FN97&appSectionid=2836&groupid=51817&subgroupid=2278&componentid=42923&make=28&model=Montana&year=2002&catalogid=2

ANy suggestions??
Thanx