Did Arbeidseinsatz workers ever drop their German captors into the wet concrete in the submarine bases under construction in France?

My Dutch grandfather Frans, who was forced to work in Brest on the construction of the Atlantic submarine bases, said that the workers would try to drop a (maybe already deceased) German in the wet concrete when noone was looking, he would say that there were a few entombed there.

I’m not sure if it was possible to get away with this with punitive measures the Germans ussually took, so maybe it was just a coping mechanism of sorts by my grandfather, but i would like to hear you guys opinion of this. Thank you!