Dynamic Roster Pipeline Ignition

I am trying to use a button to execute a pipeline. I have already set it up so that runs based on a change of a tag. What I am now trying to do is set up a dynamic rooster in order for the user to select from a drop down the people that this alert will send to. I have been able to create an array of these selected people in a custom session variable but as seen before it doesn't seem that you can reference session variables within alerts and tags. I was wondering the best way to create a custom rooster based on the drop down selection to be the recipients of the email.