Ah. You only need the keybinding portion of ahk for that. It is a whole makro and scripting language, wich would be overkill.
On mac there might even be native support for that, but my quick googling did not tell me, if that is possible for each app or only system wide. But the general idea is of course, if the small time indie dev did not bother to implement it, there are other ways of generating the required input.
I have the "problem" that while I use wasd, I use it with left pinky on a. The internet tells me, that many people use it with pinky on left shift, wich would give me cramps. I might be able to rest the finger on capslock, but, well, resting postion is with index on f. I cannot fathom why people made it left-shift-wasd and not a-esdf. Why the position change? Can't they type with 10 fingers to begin with?