i'm interested to hear more about this, i'm thinking its similar,but different to krausening. my uneducated guess would be that if you transfered enough then there would be enough yeast,especially if you stirred the cake up a bit and syphonned from the bottom?
i'm assuming its the same brew or at least similar?
i wonder if you couldn't do a swap,say,remove 2 gallons and replace that with 2 gallons of fresh?
don't take this as advise,its just musings from the top of my head
curious to hear what others think.