Can I make a suggestion? ^^
Since the Z and the S blocks are just mirrored versions of eachother, one could double as both pieces by just turning around. That means that if you had a Z/S-piece, a T-piece, an I-piece, a square-piece, and an L-piece, you'd effectively have everything covered.
Just an idea, of course. I could have sworn I saw an I-piece at the con, but I must have been mistaken. Anyway, even having three Tetris pieces is cool/funny enough.
Also, I think this YTMND is appropriate:
http://sovietetris.ytmnd.com/