Your description reminds me of an interview with Justin Roiland.



There's this guy in Rick and Morty, the rainbow suspenders football shirt afro guy. Justin, Alex and some other guy thought it would be cool to put him as a background character in all three shows, but it ended up that only Justin went with the plan.



Still, Bill DID appear in the Tiny Rick episode, plus Stan's office supplies landing in the Doopdidoo bird dimension, so there's a chance that Rick and Morty and Gravity Falls may be in the same multiverse.