[Nextgen Gallery] thumbnail "tooltip" overlay with full-size image possible?

I’m using NextGen Gallery and need to have full-size images appear in a “tooltip” or overlay when mousing over the thumbnail images. Highslide isn’t right because i need the full-size image to appear on mouseover, not click (a click will go to another page). I’d also like the same effect for the NextGen Gallery sidebar widget.

Is this possible? Has anyone done this? Any ideas would be appreciated.

Thanks!