DangerDen sells a Maze4-1 that'll accomodate a pelt, which includes the option of not running it with a pelt.
Don't you have the tapped holes under your block? There ought to be six of them.
http://www.dangerden.com/mall/blocks/maze4.asp
Otherwise, I'd consider trading it in for the 4-1 model: just call DD.
I wouldn't advise using the top screws: the clamping pressure might stress the acrylic.