Max,
I have a similar story to yours. I went to cross compile my game, was very very happy with how much time I saved by using the mingw32-* packages. And needed two more libraries that were not packaged yet.
With practically no experince packaging, I was able to create the two packages I needed in one sitting, by mostly copy-and-paste. (ie by combining parts from the .spec file from the native version of the package with a .spec file for a similar mingw32 package.) You can read my post on this list from a few days ago if you want details.
Basically, Welcome! and I encourage you to give packaging a whirl :) It gets everything in the right place for the cross-compiling stuff to just work, and increases the chances that next time you need mingw32-wxwidgets, it'll be there :)
Take care, - Jason
P.S. I didn't end up having to patch the sources at all, just make a couple .spec files. I don't know if that's usually the case or if I got lucky.