So I played a couple rounds of the game just now to get a feel for it. Could you do a timed variant of the game? As in free play on level 1 for N amount of time?
EDIT
Here's a link to the demo: http://dropzap.appspot.com/
EDIT
Here's a link to the demo: http://dropzap.appspot.com/
The Blitz version is good - one minute is enough to be addictive but leaves one unsatisfied. They've enhanced a few times to getting the complete Skinner Box effect going (I'm totally addicted to it anyway).
They also have the prize and collaboration elements encouraging ongoing participation and word-of-mouth advertising - if one plays every month a prize might be won; the more friends playing the better the prize.