Here is a suggestion. Bear in mind that the circuit has to pay a per-donation fee. There is also a nice stiff fee if people call the credit card company from home to cancel transactions.
What you do is make as many tiny donations as possible--say, a penny at a time. That will run up big bills with fees--they will lose between 35 and 65 cents per transaction, minus the penny you donate. The kicker is, once you get home, call the bank or credit card company and cancel each and every one of the transactions. The Washtowel Slaveholdery will now be hit with some nice big fat fees for such transactions. And, if anyone asks you for advice to cancel a transaction because they made a mistake, advise them that they will have to call their bank or credit card company to cancel the transaction.
The result: It will cost them more in fees to keep those machines in place than they are making in donations. It might not seem like much, but if enough penny donation transactions get cancelled at home, they could be in the hole for hundreds or thousands of toilet papers. Multiply this by only 10 people, and they could lose as much as they take in from the whole a$$embly. The more of these machines they rig up, the easier it will be to put in 80 or 90 of these penny donations (which get cancelled from home) without the hounders catching you.
What I do not advocate is tampering with the machines--you will get caught, and it is illegal (you will get sued, possibly enriching them and defeating the purpose). Putting in tiny donations and then canceling them all is not illegal--but it will be very costly to the Washtowel Slaveholdery.