How about a pitbull pleco, they get 3" max from what ive read.
Im fixated on these gobies ever since I saw a members brackish tank in the members aquarium section.
I think a pitbull plec would work. Just remember, plecs are very messy fish so I you have one you might consider overfiltering the tank and make sure you clean the substrate regularly.
So, you could do:
2 Bolivians
1 Pitbull pleco
6 bumblebee gobies
and that puts you at about 15 inches of fish, which is "fully stocked." But, of course you might be able to exceed this depending on filtration, maintenance etc. (you know that I'm sure...just stating it for the record).
If I were you I might just do a little more research on the compatibility of the bolivians and gobies just to be on the safe side. If you find info that says it might not be the best idea then you could alternate the gobies for some type of tetra.