Bilbo was able to give up the ring only because it was going to Frodo, and with much help from Gandalf.
"...its keeper never abandons it. At most he plays with the idea of handing ot on to someone else's care-and that only at an early stage...".
Frodo could have voluntarily given it up to Sam or Gollum, but I don't think he was in a state to do so anymore because I do not think he was able to exercise that much of his own free will. (He could not even keep his own hands off it, Sam had to hold them).
Rememberring that Sam held Frodo's hands to keep him from putting the ring on in the end, I think another possible answer to "How to destroy the ring?" would be that Sam could have restrained Frodo in some way (those dear Elven ropes?), and made the ring fall from Frodo (cut the chain, "dumped" it off his head, etc.) Remember the ring did not affect Sam when he wasn't in possession of it (no extra weight to carrying Frodo, in fact it was less). Or possibly when the Nazgul arrived, they would have somehow attacked Frodo in some way that he or they inadvertently lost the ring over the Cracks of Doom.
Remember that Gandalf was able to quickly return the package containing the ring to the mantle when Bilbo placed it there and it fell? I wonder if he or someone else could have quickly tossed it over the edge without ill effects?
Finally, I do not think that Gollum flung himself into the cracks of doom or that he was pushed in by some "hand of God." I think it was
the ring itself that pulled him in. After Gollum attacked Frodo just before enterring Mount Doom, Sam saw Frodo as "a figure robed in white, but at its breast it held a wheel of fire. Out of the fire there spoke a commanding voice,
" Begone, and trouble me no more! If you touch me ever again, you shall be cast yourself ino the Fire of Doom."
So, the wheel of fire, i.e. the RING ITSELF, spoke these words to Gollum, and as Gollum did not heed them, he was cast into the Fire of Doom--along with the ring. So it seems that the ring brought its fate upon itself.
We have seen in other places where evil fell upon itself to its own undoing--the orks fighting in the tower at Cirith Ungol, the two companies of orks on the plains of Mordor fighting to reach the gate first, and upon the plains when they had Merry and Pippin. Also, Saruman fighting with Sauron to both their loss. I think that is a very fitting ending here that the ring in the end destroyed itself--anyway I like it that way.
