Coin toss or a/b switch decision

Hey smart people, i have question.

I have a activated on going campagne. People enter go through some stages. But somewhere in de campagne i want to do a a/b test. I know it's possible with system program for a "normal" campagne and a/b test where you proces a batch of addresses.

In my running campagne, there are only a few addresses at once and instead of an a/b test, i would like to have a kind of coin toss or a/b switch decision.

Is this possible? and if so, who would i do something like this? If there are other ways to reach this goal i would be very interested to hear them.