[Plugin: NextGEN Gallery] different sizes for ngg images / combing ngg & wp media gallery?

I am using different image sizes in my templates which is very easy to install and configuring by adding
*add_theme_support(‘post-humbnails’)
*set_post_thumbnail_size(…)
*add_image_size(…)
to the functions.php

Unfortunatle ngg only offers the original image size (or resized one at upload) and the thumbnail-size. the wp media code for the additional image sizes (as defined in the functions.php) has no effect to ngg. is there a plungin, hack or a trick for ngg to use the wp media settings (means: creating the image-derivates, assigning images also to the wp media gallery (alias), also getting the get_the_post_thumbnail(…) work with these image derivates? before you might ask, why i am using the ngg and not only the wp media: because the ngg is a perfect solution for image slideshows and image galleries. ngg is much easier because i can group images… the wp media gallery cannot group images, etc.

http://wordpress.org/extend/plugins/nextgen-gallery/