It's possible to get WOL to work over the internet. However, does WOL even work on the LAN? Check a few things:
- Is WOL enabled in the network card's settings?
- Does WOL need to be enabled in the laptop's firmware?
- Is your laptop's software firewall blocking WOL packets?
If it works on the LAN, you're well on your way. You now need to have a router and forward the WOL traffic to the internal PC in question. Perhaps give the internal PC a static IP or a DHCP reservation so it never changes and the forwarding rule is always valid.
You can then use either this Windows based app or this web based app to wake your MacBook up remotely. There are a few other apps available to do the same thing, but you can search for those on your own.
At what point does this process break down for your?