All I can think of add a subpage and show the gallery on the "main" page.
I never needed to use multiple Gallerys.
MAybe you could use the title/description to filter.
You add the simplegallery call 2x and use JS to show only images with the title/description of "x" or "y".
Or you ask Pathologic or other developer/programmer to build a solution and pay them for it :0