Email all of a deal's contacts in a workflow rule

Email all of a deal's contacts in a workflow rule

Hi everyone, 

Right now I've got a workflow rule set up that sends an email to a deal's contact whenever a certain stage is reached.  

Unfortunately, it seems I can only send the email to one contact only.  I can add more contacts to a deal but within the workflow setup I don't see an option to email all the deal's contacts, which is what I want to do.

If anyone knows how I can email all of a deal's contacts, please let me know.

Thanks