Free printable attachments I made for Glycon (Instant mocap that uses your VR rig). You can use them for other things too, of course. You will need a bolt from a hardware store that fits the Vive trackers. I forgot to check on the exact size--I just took my tracker to a Lowes and tried out different bolts. But they should fit this printable attachment, and Bob's your uncle. Or something like that, assuming you have an uncle named Bob.
Video explaining use: