solved it with https://sourceforge.net/projects/vjoy-controller/ and then first assigning F13 to F24 to special keys on my keyboard, and then bind them in Virtual controller to vjoy. Now when pressing F13 it sends a button1 press from vjoy controller. rF2 can spot that.
Almost done with my wheel, connected to simhub. Note to others, buy an Arduino micro Pro with usb instead of a nano, then you don't have to do this workaround with vjoy. Adjustable brightness LED buttons
VoiceAttack should also do this as well as give you voice commands if you want them. I used VA with the Fanatec Universal Hub to be able to assign buttons greater than 22 and use the funky switch. Since then, I switched to my own DIY wheel with rotary encoders and now use a Teensy to handle the buttons and encoders. A plug for VA: it has a nice programming feature. Before they added Attack Mode to FE, I programmed a button to go into a boost mode (upped the power to 235kw) while the button was held down but only for 8 seconds. Further, my boost mode could only be used once every 75 seconds. That was all on one button programmed inside VA.