Using a different version of WINE/Proton could work. It may also depend on some extra utilities you need to install on your WINE prefix (Wine tricks is the tool to use for this). If that doesn’t work, the almost guaranteed to work option is a virtual machine running Windows. This comes with a small performance hit, but that may not be a concern.
Yeah, it’s an exploit but it doesn’t seem illegal. It seems like the issue is with whatever service. They need to fix their contract or their software. Maybe it is in the contract or EULA that you can’t do this sort of thing already though, in which case it’s fair game.