[Plugin: NextGEN Gallery] Question on pointing more than instance of Nextgen at the sames files?

I have a few sites that have images available using Nextgen.

I was wondering if I could combine all the files in to one repository and then point Nextgen from the different site at the common folders?

There are some files available at one site that may or may not be available at the others. I am trying to limit the number of copies of the same image files.

Thanks
Chuck