Not a simple one... you could create a separate php page to send the emails. Then load that page with an asynchronous CURL call using php.
I could help with this in a premium support ticket.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.