I use to work with Fancybox since earlier versions. What I do in that case is:
HTML:
<!-- this is the regular image -->
<a class="fancybox" href="leIMG-bigger-0.jpg" rel="leGallery"><img src="leIMG-0.jpg" alt=""></a>
<!-- this is the rest of the gallery... hidden -->
<div class="fancyboxHidden">
<a class="fancybox" href="otherIMG-bigger-1.jpg" rel="leGallery">
<img src="otherIMG-1.jpg" alt="">
</a>
<a class="fancybox" href="otherIMG-bigger-2.jpg" rel="leGallery">
<img src="otherIMG-2.jpg" alt="">
</a>
<a class="fancybox" href="otherIMG-bigger-3.jpg" rel="leGallery">
<img src="otherIMG-3.jpg" alt="">
</a>
<div>
CSS:
.fancyboxHidden {display:none;}
This way you are:
1) Using your full gallery (try the thumbs helper and will look great)
2) Indexing all the images for search engines
Hope this will help you, for a good example of this check out this site in source view.
PS: There is many ways to achieve what you want, you can create the gallery directly from JS or combine both ways. This is the way I choose for image indexing ;)