You can't open the back of the drum but you could remove the heater element or sump hose to retreive it. Depends on how mechanically minded you are. Be sure to turn the power off & pull the plug before doing anything.
Bra wires (or any other foreign object for that matter) stuck between the drum & tub is bad news. It can destroy your heater element. If a coin gets stuck in there it can actually punch a hole in the tub.
Mike
October 2009