Though this would take some work, I don't think it's entirely impossible.
I noticed this on amazon..
Amazon.com: Bosch DLR130K Digital Distance Measurer Kit: Home Improvement
It only measures 4 inches tall. I know there would be no way that the unit could fit inside the helmet stock, but I do wonder if you could separate the pieces and say place the laser and receiver in the stalk then run wires down to the rest of the unit which could be taken further apart (like separating the battery compartment/keypad/etc) and placed inside the helmet.