Hello apoca1ypto,
I apologize for my late reply.
Unfortunately whole operation is not that easy to solve. You can't just provide image path where image name is. It's all because default script looks for images only in current page:
{{ page.media[element.image].resize(270, 190).html() }}
It's possible to search for images in other pages by using something like that:
{{ page.find('/my/other/page').media[element.image].resize(270, 190).html() }}
But that would work only for specified page. Allowing to use different directories would require rewriting whole gallery script, but it's possible of course.
For now, I would suggest simply use different image names. Much easier and still you can achieve what you want.