This repo is for you. it is a customizable, remappable xinput mapper for the wii balance board. It uses standard python blueototh and HID libraries. Made specifically for a specific rhythm game i wanted to play, so I can't guarantee it'll fit your needs, but feel free to fork it.
step 1. download the requirements in requirements.txt (pip install so and so). (or python if yu havent already somehow) step 2. remove the wii balance board from your bluetooth (if its there) step 3. re-connect yuor balance board to your computer. on windows, you have to use control panel > add a device because its the only way to pair without a pin. step 4. run python .\run_wbb_gui_qt.py step 5. Tare yuor board. wait a few seconds step 6. now you can mess with whatever settings you want and itll pretend to be an xinput controller. enjoy.