Got it figured out with jquery, the code below will grab the text of the caption and insert it as the title attribute as desired.
jQuery( "span.collage-caption" ).each(function() {
var titleattr = jQuery(this).text();
jQuery(this).prev().attr('title', titleattr);
});
Anyway, it would be nice to have a similar option to enable / disable this feature on the shortcode` (show title on enlarged image)
