I just run on two mini PCs.

One running OPNsense, fanless N5105, 4x 2.5Gb, it doesn’t need much disk or memory but at the time it was a negligible additional cost to go to 16GB and 500GB.

The other is running Proxmox, on a Ryzen 7 7840HS, 96GB RAM, 500GB SSD, and with two 5TB USB HDDs plugged in (rotated with a third that I keep at a friend’s place as a cheap but fit for purpose offsite backup).

It’s just them plus a managed 2.5Gb switch and a couple of wifi routers in AP-only mode. It costs very little to run power-wise and is more than enough grunt for my needs.

Booting on a schedule as others have suggested would be the simplest by far.

To answer as asked though, it’s not something I’ve needed to do but it sounds like a VPN + IGMP proxy (I’m assuming you have a separate subnet for your VPN) might fit the bill.

Alternatively some kind of low power device (a Pi or something) that lives in the same subnet could make the WOL call locally, and you just need to find a way to trigger it. Could do it via a http call for example.