Links to external websites – NextGEN

Can someone please tell me if it is possible to create a link through to an external website with NextGEN using the Alt & Title Text or Description field? It would only be for some titles that would show a screen shot of a website then I would like to link through to the website.

I have tried custom fields but things are going screwy with that ie. although the link works properly on the front end, the link repeats itself four times in the back end and mucks up the first thumbnail.