I use OpenVPN myself for WOL purposes. But for many years, I used the following, and it worked just fine.
forum.dd-wrt.com
Only difference is I changed the external port (9) to something more obscure (e.g., 20999), and unlikely to be blocked by the ISP (many ISP's block some of these low-numbered ports).
I would also use the following online service to trigger the WOL, where m is the mac address, i is the domain name (or explicit public IP), and p is the external port.
Code:
https://www.depicus.com/wake-on-lan/woli?m=010203040506&i=mydomain.dynet.com&s=255.255.255.255&p=20999
Drop the link on the desktop and all the user has to do is click it.