Update: Yeah, dang, it doesn’t work.
Observations: The lid bulges, but no movement of liquid. I have to press really hard on the lid for even the slightest flow towards the can. As this is probably going to be a rather light beer, I don’t expect much more CO2 buildup.
Theory: There is too much air in the system. The CO2 from the fermentation increases the pressure in the keg & lines, but not beyond the compressibility of the gases involved.

Now I hope I have not spoiled my beer by exposing it to too much oxygen. I’ll probably get a bubbler ready tomorrow and just purge the keg with CO2 from my regular source.
Most of this setup sets me right on track though to do a oxygen free transfer though, so not all was in vain - given that I haven’t spoiled my brew. /o\