Drilled a few holes in my palm rest and press-fit a few ~4mm lengths of thick plastic fiber optic strand I had lying around:

[above: crappy light pipes installed, BMP messed with until all four LEDs light up. Left to right: power (green), error (red), activity (orange), usb-serial (yellow).

I may update this in the future if I end up trying it out with other Thinkpads, but for now this project is getting switched to 'complete'.