Get him (or make, if you are creative) glove puppets of characters or creatures that he likes, and improvise a 'puppet theatre' from chairs or an old fashioned clothes horse (beware of trapped fingers though) with sheets or old curtains over them. If he can't dream up a 'script' himself, give him some ideas. Invite a few similar-age children round, and they can put on a show for parents. If they like music, it could be a concert, X-Factor or The Voice, or whatever.
Help him open his own 'cafe', with little sandwiches, biscuits, cakes etc, and healthy drinks. Make 'play money' (or use toy money if you have it) and cash register etc. Again, invite friends to come to the cafe, and children could take it in turn to be waiter/waitress, cook, etc. Plenty of TV programmes to inspire a setting, menu, etc.
Also: travel agency with brochures, maps, timetables. Or airport terminal, with check-in, luggage etc. If you know any books or stories in any similar settings, incorporate those as well.
Or Space Station, space travel, other planets etc. Plenty of web sites on all of that stuff; improvise bikes, ride on toys disguised as space ships.
(I didn't work twenty plus years in Infant School/Nursery for nothing you know!)