I've discovered that you can use %COMPUTERNAME% in the Favourites list:
Favorites SHOWICONS NOOPENINTABS PATH *%COMPUTERNAME%
This only shows favourites within a branch with the name of the current computer - really useful if you share config between two machines but the favourites are different on each.
However, I'd also like the 'Add to favourites' command to default to putting the favourite in the same 'computer name' folder - but I can't see how to do that.
The Add command I currently have is the default of: