Why don't you set the editor size manually? That way you'll always know how big the lightbox needs to be.
Alternatively, I'm sure you could pre-create and hide the editor instance (Or really do anything with DOM you need to do to get it to play nicely with lightbox). I know that highslide has some documentation on loading pages with AJAX calls, so the problem may actually be your lightbox plugins problem, since it might just need to wait for the editor to load.
Check out the sample pages in your CKEditor folder under: _samples/ajax.html ... perhaps that will help?
Re: Preload editor to fix lightbox positioning
Alternatively, I'm sure you could pre-create and hide the editor instance (Or really do anything with DOM you need to do to get it to play nicely with lightbox). I know that highslide has some documentation on loading pages with AJAX calls, so the problem may actually be your lightbox plugins problem, since it might just need to wait for the editor to load.
Check out the sample pages in your CKEditor folder under:
_samples/ajax.html ... perhaps that will help?