This may be fanciful and not practical at all, but have you looked into using the microphones to detect taps (along with the trackpad)?
I feel like it could help discriminate voluntary taps from accidental brushes by requiring a minimum impact on the trackpad
It might even be possible to use triangulation to detect taps on the laptop body, although it seems harder than just detecting a brief sound that's synchronized with a tap on the trackpad
I realize there are privacy concerns, and that the recording indicator would have to stay on
Also it wouldn't work in noisy environments obviously