Just get him to wear loose fitting shorts on top. I wear both - the Lycra with the shorts on top and hubby does the same. All made by Altura the cycling company / they're listed as baggy cycling shorts that you fir the Lycra lining underneath.
The Lycra ones alone also go see through on the bottom sometimes so I have no idea why more people don't cover up.
We have a couple of dads in inappropriate Lycra at school and it's not what you want to see 1st thing in the morning!