I've tried, I've tried... but I find no way. At least no automatic way. You can make a Yam Yam which has an active shield and a rock. Then the player can walk around the Yam Yam and collecting more and more shields, while the Yam Yam creates more and more rocks.
It is possible.......just. It's not very fast but is pretty much infinite and requires no player intervention.
It has to use a yamyam (only one page), fast amoeba (turns to rocks) and a diamond...... I like these kind of mini challenges as they're almost like puzzles themselves.