Never dealt with a broken mirror, so I can 't helptoo much. If the dealer says the glass can not be replaced alone then I'd replace the whole unit. However, if you have access to a blower heat gun, (looks like a hair dryer that is used in the electronics industry) you might be able to loosen the tape that holds the mirror to the mechanical housing. but make sure before you do that you have either an extra mirror or housing on hand incase it does not work.
Craftsman 27801 1500 watt Heavy-Duty Heat Gun at Sears.com
Frank