I don't think there is any other way to include the special_galleries.php file than make your own galleries page. I tried it with php include File and that did nothing.
You can always hack the file to add your test @ ~ line 129
This is one of the "fragmented" problems with gpEasy. Pages outside of the /data/_pages/ folder can't be used via functions like File Inclusion. This is true for the blog, contact page, and extra content areas as well. . .