How about on the checkout page, there is a checkbox for "send me a charger" and it is unchecked by default, which also applies a $20 discount in your cart. You can leave it unchecked, accept the discount, and not get a charger (which most people will do since it is the default), or you can check it and get a separate $20 charger sent to you along with your iPhone (pretty much the same as if you added one to your cart during checkout today).
This would be the reasonable approach. But Apple won't do that because it is entirely about the money.
Why would they do this when a 5W USB charger costs no more than $1 or $2 to make?
Buyers are already effectively getting a discount as prices haven’t increased with inflation; the $999 price of the XS would be $1137.77 today. Yet the 13pro remains $999.