This definitely isn't the best looking solution, but it works well.
I actually designed my own Leap Motion mount out of cardboard, and taped it to the front of my google cardboard. It's very sturdy and secure, none of the sensors get covered, and you can still access the cable port.
Here's the design and specifics:
(Just incase you can't read my bad handwriting, the area between the bottom of the mount and the bottom of the slit is 0.5 cm tall, and the slit itself is 1cm wide)