House key case

Spray the upper surface of the key with hairspray, or otherwise treat it to make it a sticky printing surface using glue or kapton tape, before inserting the key into the printed part.

Layer height needs to be 0.25 mm. Edit your gcode to pause at the start of layer 12, when Z=3.25, so you can insert the key into the partially-printed part:

G1 X0 Y0 F5000 ; move out of the way
M0 ; pause to insert key

This will move the print head to the home position when the printer is ready for you to place the key into the print. Insert the key. Then hit the "resume print" button to start the process of cocooning your key within the printed shell.