I'm not sure if you've tried this yet but you can modify the website for your acknowledge alert. If you open the Solarwinds Database Manager and drill down to the Websites table in the NetPerfMon DB, query it as Read-Write and change the ServerName to your FQDN instead of the server name and the IP address with your public IP. If you require a secure connection back, put a 1 for SSLEnabled and you should be good.
I had a similar issue since we have to acknowledge alerts from outside our domain
Thanks for posting Derik, most of these are already on our list to add in a future release.
How bout a 20 or 50 element Lab License with the purchase of an SLX license???