Failed Parti-gayle -- Starter?

Brewed a hobgoblin clone today, and was going to use the third runnings as a parti-gayle. Third runnings ended up being only about 4 gallons at 1.020, will this work to build a decent enough yeast cake to pitch a nut brown ale onto? Or not enough sugar to work with?

when that happens i just boil it down with a fan blowing accross it to increase evaporation. Some might consider this a waste of propane/time, but it sure is nice to have a little low ABV session brew or/and i'll throw some in a milk jug in the keezer. when its time to make a starter its no work or cost, and i can make it as big as i want. I always do this with larger brews. my last came in at 1.026 IIRC, tastes great.