[Plugin: NextGEN Gallery] Random picture in page w full-size image

[I’m reposting this cause I think I originally posted in the wrong place in the wrong tittle]

I seem to be so close to achieving what I need to, which just in case is:
– ONE random image from a specific gallery that can be displayed at full size (not thumbnail size) in the body of my page (not the sidebar).

I’m using the following shortcode in the page in question:
[random max=1 w=850 h=480 id=42]
and it works expect it totally ignores my size requirements.

Is this function only working with thumbnails? It looks that way. If so, how can I change this in an upgrade-friendly way?

Thanks!!