A very thin sheet of acrylic glass would do the trick, though I have to stress that this may result in performance and accuracy issues. A lot of it depends on the lighting environment, which can cause false positives or other tracking issues if light were reflected off the pane. Smudges and scratches on the acrylic would also further detract from tracking quality.
Ultimately, accuracy takes a hit when you place something between the hands and the device. Is it worth it? For your purposes, it depends on the distance of the interaction zone that you intend to use, the environmental lighting factors, and your priorities in the design of the installation.