If he's going to jelly park their signs state no cloth nappies.
It might be more discreet for him to use spouse ones, then he can change in a toilet and chuck them in the bin. Its the kind of thing I could imagine (for my DS anyway), that would fall out of his bag then he would be baby nappy boy or something like that
If it helps at all, DS1 was exactly the same and he's just started to come right. How many times a day is he having issues? You can PM if you want