How do I set a Randomizer to allocate a subset of scenarios first until a target is achieved?

My survey has 12 scenario blocks. I would like to randomly allocate the blocks so that each participant only views one scenario. Is there a way of setting the Randomizer such that any 2 scenarios are presented first until I have a fixed number (say 100) of responses per scenario before the rest of the scenarios are allocated. My goal is to have 100 responses per scenario which will give me 1200 responses. However, if the response rate is low, I would like to get 100 responses for any 2 scenarios before the rest of the scenarios are presented. Any idea how I can achieve this?