Simple answer: Put the fronters in separate campaigns. Each campaign can then have a limited list of "Closers".
If that's not possible ... re-examine why it's not possible and make a change so it IS possible. LOL
Reality Check: Please define "which type of phone call they are on". Technically. Remember that Vicidial is not listening to the call and catching keywords like "insurance" vs "Vacation". So: How would Vicidial know "which type of phone call they are on"?
There are some more complex options, such as the Agent API with a web page in the Script pane making the decision based on selections made before the call terminated and/or values in the Lead record. Moving the transfer button into that page would allow the Agent API to initiate the transfer (agent still pushes a button, but it would be a big red button that says "Transfer!" and would make the decision instead of the agent "where" to send the call.