How can I fix a leaking shower drain that is not accessible ?

I have a stand up shower that has a small leak in the drain. It drips underneath to the first floor. Upon removing the ceiling tiles there is simply no way to access the PVC pipe because of the floor joists. Fixing it from the top is preferable, but tearing out the shower floor is not an option. Is there perhaps some sort of sealant that can be poured down the drain, or perhaps a fix I can't see? I can see the leak. And it appears to be a union between two pieces.