[Plugin: NextGEN Gallery] how to add “x close” function in slideshow browser?

Situation:
When you view in PicLens, there’s an “X” in the upper right hand corner that closes the slideshow. Alternatively, when you click an image from the gallery, you view the default slideshow, but there is no “X”–instead you have to click the image to close it and go back to the gallery.

Question:
I’d like to customize this default viewer so that I can put an “X” or “X Close” on the screen to make it more intuitive for novice web users. After looking through the source files, however, I’m unsure how to do this. Any ideas?

Using NextGen 1.2.1, WP 2.7.1, [nggallery id=x] to display gallery.