Yup most internal routing arrangements have a small tube inside to guide the cable. My gios has simple slots in the TT to pass the entire housing, but they are reinforced at the periphery. And a tight rubber grommet.

I've seen some Mieles and Miyatas with simpler non-reinforced slots w. a grommet. Not sure if it's a good idea in terms of keeping structural integrity. I think I heard somewhere that they sometimes failed. So a DIY hole is probably a bad idea.

BTW the OP's picture is of the type with a tube within the TT I think.