I’m going to venture a guess and say… no, it’s not possible. I don’t know for sure though.
The problem is how the signals get into the Wii and then into your computer. The Wii doesn’t provide a direct route to send its signals in, so you have to do a workaround (aka.wiimote) to get anything at all. Then connecting the balance boards? If they don’t provide an easy way, you’d have to do some kind of hack, which may yet be impossible too.
I do wish that ALL new hardware for human-computer interaction came with either a MIDI out or a USB out that was recognized as a standard input, which Max (and lots of other programs) could read as MIDI or through [serial]. But companies seem to be too proprietary with these things, and I really don’t understand why… is it really a problem for them if people want to buy a Wii Balance Board for a musical performance, rather than use it as originally intended? Sheesh, we just want the hardware, and we’re willing to pay. More sales for them.
I also found this highly annoying with the Rock Band drumset. There is a hack to get the data into your computer, but man, put a MIDI Out on it already, so it works out of the box. Then you’ve got a low-cost MIDI triggering drum set, which lets you do pretty much anything via your computer. But, NO……