Different sizes for highlights and thumbnails?

Now that I have the ideas from this thread working, I'd like to do something related -- how do I specify a different size for album highlights than the normal thumbnails? I searched in the forums but couldn't find anything.

For example, my current thumbnails are set for 75 (square), and each album displays as 75 square, but I would like the album highlight to be 150. Oddly, the highlight for the root gallery is already 150 (as seen in browser source), but I can't figure out how to override the default dimensions in the script g->image call for any other albums.

Can it be done?

Thanks.