H.W.
If it were me, I'd adjust the home nap, or be prepared to have him go to bed earlier on preschool days, since it's only two days a week. Tough call! As a former toddler teacher, it is more difficult for us to have a no-napper at this age, but after the 'usual' nappers were asleep, we'd let them look at books on their cot or play quietly at the table.
If you are really wanting him to nap at school, then yes, adjust the home schedule. Get him up earlier if need be/doable for you.