They would be traces with pretty obvious patterns and easy to cut.

But I don't the GP comment was talking about that; I have also used WiFi without an antenna (PCB or otherwise), and it was also slow for me.

A dummy load is probably the best idea: an impedance mismatch would obliterate any chance of anything working (including Bluetooth fwiw).

The point of a dummy load is to match the impedance so that all the radiative energy gets turned into heat and the transmitter is none the wiser.