You're pretty much out of luck.
The whole idea behind removing a battery following a liquid spill is that it allows you to immediately cut all power to the machine, which reduces the risk of a short (which can irreparably fry the machine).
With a built-in battery, there's no way you're getting that battery out in time to prevent a short. They're a PITA to remove, especially now that even the external enclosure uses security screws.
Theoretically the power button should shut off the machine if you hold it down long enough, even if the machine is completely locked up.