>He put lead into mold
I like it. I never thought of this line and was happy with what you got.
Yes there is no fun in the final product. There can't be.
I am intrigued by your change in the game. What you are doing is a kind of choice to the next player. The skill lies in not writing the line but choosing the choices. This way the first player has most control over the rhyme. (We might get a good rhyme out of this. Let's check)
Tried and failed do it. How can we give choices to the b rhyme. The whole dictionary is a choice.
Anyway here goes:

A parachute fell from the sky.
xxxxxxxxxxxa
xxxxxxb
xxxxxxb
Proving indeed that pigs can fly.