Currently there are no gateway fees, and any gateway can be used for any term that is assigned to an order form. I suppose it would be possible to create packages with yearly terms on a separate order form that has PayPal while packages that only have shorter terms are on another order form without PayPal.
We have a task, CORE-2305 that would allow discounts on gateways. Would this accomplish what you're after, by discounting non-PayPal gateways and adding the fee into the price of the Package?
Some payment providers have rules against adding fees for using their payment method.