you could always stack an M1 or dingo(idk if either is a mod) but take the axle off a pgm and put it on the one drop(thats what i did at least) if you want ill post pictures
I used to have a stacked m1. you just do what toasted said. take the axle from a pgm and put it on. fits like a glove apparently. I didn’t do the modding myself, but I’ve heard that it’s not too hard.
Also as said before, werrd yoyos are often stackable. the rozzor 2, 4xl, split d, etc all have posts for jimmy hats.