Old sock -
I really dont want to add any fruit. I am too worried that it will impart flavors that will compete with yeast and sourness. Honey may not be bad - but would the regular yeast (sach?) just eat that? Same with DME? Add why would it add the flavor of sugar? Would all the sugars be eaten between the yeast and the bugs?
At this point the Sacch probably isn't as active as the Brett and bacteria, so they should eat most of whatever sugar you add. What I was trying to say is that I generally don't add a sugar source simply for the fermentables; I add fruit if I want to add a fruit flavor or honey if I want some honey aromatics.
Malto-dextrin or lactose certainly could work, I just haven't tried them.