Assuming you're talking about the type that need to be VERY ripe, I think the Hachiya variety, you need only peel them, locate the 4 “plates” (the tougher parts) and remove them. The rest of the ooey goo you refer to is what you'll use for bread, cookies, etc. You can freeze them right off the tree and blanch them to get the skin off, but you'll still need to locate the plates and discard them.
Just be glad you got them before they got the chance to Splat on the ground. They can be even worse to try and clean up!