Playlist thumbnail size & spacing

I've been scanning the forums and various web resources for help on changing the way the playlist looks with a given skin. With any skin it looks like the default is the thumbnails displaying at 60x45 and pushed right up against one another. I would like to be able to change the thumbnail size to 60x60, and add more space between the thumbnails (or more accurately, I guess, increase the space between playlist items.)

I've tried adding to the height of item and itemOver.png files for the skin I'm using but that appears to have had no effect.

Is this something I will need to do in Flash, with a copy of Flash? Or is there some sort of way to change the configuration without that?

Thanks in advance!