That is exactly why I bought the 1 liter solution so I would have 500 ml of stabilizer stock. I think in your instance, you might need even more since your 120 needs 590ml of stock and your 2 roll needs almost 700ml.
My tank only needs 500ml of stock to do 2 35mm and 1 roll of 120 so I was able to just use the medium Rollei Digibase kit.
So in your situation, you might want to buy something like this also and mix up 1 liter of stabilizer? I think I saw someone saying that in this thread as a solution. I dont believe in the US you can buy just the Rollei stabilizer but the Kodak should work?