you should be able to find something around the house that will fit into the slots. if not just go to a local stereo shop and ask them. they should be able to do it for free, just tip them a buck or two to be nice.
Don't use two butter knives, that will wreck the cage. Trust me, I have a jvc deck and my cage is messed up so now i have to use screws to lodge it in there. Just go to a car audio shop and say you lost they keys to ur deck and they might even just give you a set.