I'm sorry, but double clicking is pretty much impossible with this thing. Thank goodness we don't need to double click for anything.
I looked through the whole "Input" menu. Not one way to map double click (or anything) to one button. I hear if you hold the controller against the desk or with your other hand... you MIGHT be able to stabilize it enough to click twice in one place. It's such a shame our fingers movements all happen through our wrists- kind of makes your hand move. I think this works out well for me in every other aspect of my life except for VR desktop.
Mind you, only one specific bluetooth keyboard works with the new keyboard pass through feature right now. Annoyingly. So you'd better be good at touch typing if you use one. Personally, I'm hoping my Arteck keyboard gets added in the near future. I like having a full sized keyboard. Which the Logitech K830 isn't.