I have found in the past where the wife is uuuuuuuuuuuuuuuu of reluctant to have extra fun the best way forward is slowly but surely, allowing the "new guy"  to view the fun 1st , maybe even taking a few pixs for the couple, having the guy view would go a long way to relax her enough , everything at her speed and to her liking , slowly the guy could join in after building up trust,  

I have found in the past where the wife is unsure or reluctant

sweet, thanks for the tip