Is it just some 2 pin connector or something more sophisticated because of the fingerprint reader?
Its been a while since I've tried it, and never tried it on a more modern machine. But the connector is more than just 2 pins. But the actual power button should just be shorting two pins. Since you won't have the keyboard you won't have a way to probe for which pins do the power. But if I remember right the power/fingerprint button gets merged with the flex cable for the touch pad so there's a lot of pins to probe. Looking at photos online of the palm rest I'm not seeing a dedicated power button connection so that appears to be the case for that one too.
Good news is that google says if you remove all power and plug it in the machine should turn on. So just make sure you configure power on when plugged in and you should be good.
But a bonus issue is you may get the "system configuration invalid" error my T14 gets every time it reboots. I get the error because I swapped the main board from a T16 into my T14. IDK if not having a chassis will trigger that alarm. But it's incredibly obnoxious and I never got around to trying to fix that.