Hi, yes you can. Fancybox does not use thumbnails at all. It just needs a link (URL) to each image. It does not care if it is text, a thumbnail or even an empty anchor, as long as it is linked to a large (full-size) image. It will also
Here is an example to paste in a text widget:
<a href="https://url.of/first/image.jpg" title="Title of first image" rel="my_gallery">View gallery</a>
<a href="https://url.of/second/image.jpg" title="Title of second image" rel="my_gallery"></a>
<a href="https://url.of/third/image.jpg" title="Title of third image" rel="my_gallery"></a>
Replace the URLs in the href attributes with existing large or full-size image locations (they do not even need to be hosted on your own site so if you have a Flickr or Picasa/G+ account for example, you should be able find their public URLs) and give each one a meaningful title in the title="" attribute.
