You can try to use a credit card and slide it under his foot but this is said with great care, you may damage his foot if you are to rough with him. Another meathod that has worked for me in the past is to put rubber gloves on just a pre caution, you may not want to wear them as i don't but you be the judge. Just gentlly message his foot back and forth in a proding motion which will make him loosen his grip.