Wild and Crazy Ideas

So the Payload thread got me thinking...
I need a demo unit for a class I teach on proximity sensors. One type of sensor we talks about is capacitive. They work on a principle that capacitance changes with changes in dielectric constant of target material vs Air (which is 1.0) Most plastics are around 2 which is not enough to trigger the sensor... a good thing.
Water is 80 so my thinking is making 2 test pieces that look the same externally 5 mm thick with 25% Fill so mostly air in the core and a second piece where I pause the print and fill or partially fill the core with water before finishing the final layers.
If printing PLA the bed temp does not matter so provided I am not trying to lay the next layer on water it should bond right?
I have already proved the concept by filling a calibration cube with water and having it trigger the sensor vs the empty cube.

Am I mad to even consider this?