Allow Asset to use different ports

I have Asset installed on a Windows laptop, as well as now on a Macbook. I can see both of the servers on my internal network without any issues.

After a lot of stumbling around, I've figured out that I can't access both of the installations from the internet, since both instances use the same port (26125). Apparently, a router can only be configured to forward a call to a given port to only one IP. Is there any way to change the default port of one of the instances so that I can access both Asset servers externally?

UPnP cannot work like this, because it works on network discovery and broadcasting to the whole network.