Yes, for Therians the PIDRNG frame advances as if there was a gendered Pokémon in the first slot (so an additional + 7 advances overall.) I'm not sure why it does this, but the game acts this way consistently for me at least, so it should work for you to. It is best to do a 'trial run' first by receiving a slot 2 Pokémon with the first slot occupied by a gendered Pokémon, that way you can test out whether your calculations and seed work as expected beforehand.
Hi, you pretty much gave me the idea of looking into Pickup RNG.
I've been looking at some things.
Basically, if you do lots of consecutive battles using sweet scent straight after teh previous one, you'll find that the Pokémon you battle is 6 frames after the previous one. The fifth frame, i.e. the one right before the next battle is the Pickup RNG Seed.
You don't need to copy the seed and paste it into the researcher again. You will notice that all the frames that come after a certain frame are the same frames that would appear if the number of that frame was the seed.
So basically rather than putting that seed in the researcher again just look at the next 6 frames or so.