Oh, here is an important question:
You say you can't enter them with Alt+Letter, but that may be because the hotkeys are being intercepted.
Can you try this for me, in notepad, generate a set of your letters, and then try to copy and paste into farr search, and tell me how that works.
The goal here is to figure out if farr behaves the way you need EXCEPT for being able to generate the letters with alt+Letter, or if the problem is deeper.