Which spacer did you try?

I drew up this spacer for the z-axis switch: http://www.thingiverse.com/thing:440022

It fits my pro nicely, and can be adjusted in scad to change thickness to acommodate the thickness of your glass.

I like that it drops in and is removable (for different thicknesses). No offense to the switch-moving thing, but I wanted to have something less intrusive.

There's a comment about it not fitting one guys printer, but it fit both my creator x and my pro, so I don't know what to tell you about that.

There are a couple of other 'sit on the back of the z-axis plate' spacers on thingiverse, too, if you don't like this one.

Cheers,

John