Hey EPBrassil, conveniently next gen does have a function included which allows you to do such a thing (if you haven’t figured it out already) In the wp-admin Next Gen Gallery dropdown, select manage gallery, select whichever gallery you would like to work with, on the top right of the options area you should see an area that says ‘page links to:’ select which page from your database you would like the thumbnail to link to.
I should note, that as far as I know, this feature applies to gallery thumbnails and links when you are viewing them in an album, though I have not tested this feature beyond this capacity. Also, in the wp-admin gallery drop down under: Options > Gallery, ensure that ‘Deactivate gallery page link’ IS NOT selected.
Cheers