Macro to activate keystroke on press, and again on lift

A quick example of what my problem is and what I want to do. The game I am playing has a lock-on target mechanic that toggles onto a target with a single key press. But there is no way to select the next target without unlocking from the first. This means, in order to lock onto a second target, I have to press the button three times. Once to lock onto the first, a second time to unlock, and a third to lock onto the next.

I would like to activate lock-on when I press the button down, and deactivate lock-on when I lift off of the button.

This would essentially function like the "Hypershift" key but with a keystroke input that the game can read.

If anyone would tell me how to do this, that would be great! If you know it's not possible with the software, please tell me that too so I can stop searching.