It isn't possible to port forward to broadcast addresses, the OS blocks the attempt for security reasons. I tried to get this working several years ago, but ran into that wall. You need to either use the web interface, (which can be scripted with curl,wget, etc) or ssh in and use the wakeonlan command(also can be scripted), or install some sort of proxy that will handle rebroadcasting the wake on lan packets.
I went with the curl + webgui method. You can create a user that only has access to the WOL page, to reduce the security risk of having your admin password in a script.