Basically every game works with it. The number of games that don't have an off-screen function is less common, and right click is the standardI had no idea this is how they worked, I thought it was all up to the game to know when it was off screen. Well I certainly learned something and the guns are smarter than I thought!
With trigger, grip and trackpad that's still 3 usable buttons I can remap through OpenVR2Key because SteamVR still sees them fine.So I had a look at OpenVR2Key, I hadn't seen it before and I didn't realise it was open source. I setup my vive controller but thought I was going to have an issue as you said it needed an Index controller to map and he mentions that's what he has.
But I found he did try to support Vive at one point but the releases page is a very old build. So I compiled the code and was surprised to see it was working now.
I dug around a bit in the code and figured I could probably make mouse clicks work but would need to hijack some keyboard keys to test it quickly and not bother with the user interface side of that.
So I've mapped F1 to left mouse, F2 to right mouse and F3 to middle mouse.
I'm attaching my build of the exe and the source code.