Mr. Harper says the customers welcome the preservation fee almost as though they were purchasing a product. In this case the product is preservation, and the customers sympathize with the need for preservation. So instead of a mandatory 5% fee, why not market preservation as though it were a product like a book, T-shirt, poster, or other souvenir?
C&TS could sell handsome certificates showing a patron’s contribution to the preservation effort, and price them in multiple denominations such as $5, $10, $15, $25. Most people would probably not want to buy the cheapest denomination. Many would probably buy the most expensive one. If they want to donate more, they would just buy multiple certificates.
If the customer truly does welcome the preservation fee, there should be no need to make it compulsory. And by opening this up as a voluntary donation, even though not every rider will donate, the overall amount collected would probably far exceed the straight 5% fee on all riders. And best of all, everybody would feel good about it whether they wanted to participate or not.