I don’t think you could bind it in 0.3 or earlier. From my understanding, LK3 acts as a duplicate shift key.
On that note, LK1, 2, 4 and 5 can all be achieved by pushing shift and ABXY. It’s more of a convenience thing. I’ve actually taken to not using it, preferring clean lines and a streamlined system.
It may be possible to reprogram the arduino board, removing use of the shift key altogether. You would only be missing out on the + / - keybinding, which is usually for volume control. But with the universal hotkey to control brightness and volume using select and the D-pad, it becomes redundant.
In short, you could map shift to either + or -, and map that key to whatever you want.
I haven’t checked it, but I assume that LK3 is potentially hardwired to be the same key as whatever shift is, so you would need to have this duplicated.