Pitching Dregs Post Fermentation / End of fermentation

So i have 6 gallons of an imperial stout that i dont really want 6 gallons of, rather 5, so i am thinking of experimenting with the extra gallon.

Fermentation has already halted / is coming to an end with an OG of 1090 and gravity reading as of today around 1020 (not as low as i would want but its slowly getting lower)

my question now is, can i still pitch the dregs from say a russian river or jolly pumpkin beer in one gallon of this beer and see any results (even if the resulting beer sucks, i am just trying something new).

I did exactly this with a robust porter that I had. I added cherries to one gallon of it and then pitched the dregs from a Jolly Pumpkin Bier de Mars. It soured really fast, like 2-3 months, and turned out to be one of my best beers. it is definitely worth trying especially if your just using a gallon.