I use a really simple AutoHotkey script to send my numpad key presses to Gazō Tuber even when I have some other window in focus. If you're interested: https://drive.google.com/file/d/1vyrpqycn1ZQgIqAvkrqA-RRAd5mCVEv5/view?usp=shari...
(It also translates them to function key presses, because I wrote it before Ai Risun updated the program to use numpad for presets too. So it could be simplified even further if you wanted!)
It works like a charm for me. If you have separate a bluetooth/USB numpad, it's like a desperately low-budget Stream Deck :p