Just replace line 94 of wp-content/plugins/nextgen-imageflow/lib/functions.php with:
$out .= "\n\t\t\t" . ', onClick: function() { return hs.expand(this,{ src: this.getAttribute(' . '\'longdesc\'' . ')});}';
Then set the ‘onClick Behavior’ setting of ImageFlow General Settings to a value of ‘other’. ( You can use any text, other then the default of ‘function() { document.location = this.url; }’)
Should be all you need. It worked for me.