Hi holch,
Did you manage to implement it using tokens? I am trying to do something similar. I want the survey to be anonymous and I only want a limited number of subjects to participate, let's say 100. For 50 of them I want the variable (let's call it GroupRole) to take one value, say 1, and for the other 50 I want GroupRole to take value 2. Since I want the survey to be anonymous this means that any new user generates a new token (by introducing an e-mail account in the initial page), but for which the value of GroupRole is not defined... Did you run into a similar problem? Thanks for any feedback.