In addition to the thread reply you got (noting you'll have to manually add it somewhere using something like AdvanceMap or editing in YAPE, the latter which I've never done and has more likelihood of destroying something else), I can tell you that I'm working on a bugfix version that also solves this Froslass problem; I'll have it added to one of the wintery areas. The person who tested it for me reported back that she got her Froslass, so I am happy that it's working.
When a future beta comes out, you'll be able to find it. :)