Help with shortcodes and <!–nextpage–>

I’ve wrote a plugin that uses shortcodes.

My plugin do the following:

Through the shortcode [album id=x] the plugin fetch some images from a gallery script that I wrote and output the images

I’d like to add a pagination with <!–nextpage–> tag, for example: if the images are > 20 print ‘<!–nextpage–‘;

The problem is that the output are already parsed throug wordpress and I get only the code

i.e.: <img src=”x><img src=”x> <!–nextpage–><img src=”x><img src=”x>

Is it possible to parse the <!–nextpage–> shortcode in the output?

I hope someone can help me ??