Last I enquired of Northern (a few months ago) the answer was no. They said they were expecting it to be added - along with TrainCards and County Cards - in a software update.
Get a Promise to Pay, and get one from the guard. Just to be safe, I would make sure you pay the guard in cash, if you can.
There is no obligation for the OP to pay cash to the guard.
He can pay by card or cash if he wishes.
What is a promise to pay voucher/ticket, are these free?
Seems odd that you need to pay cash to the guard, I thought the train companies were trying to encourage pre-payment and electronic payment?
Yes, at penalty fare stations you are able to get a promise to pay from the machines, it's quite convoluted to get one unfortunately. On the screen it should give you a promise to pay option, press it and it will explain what one is and then give you the normal interface where you are able to choose which station you would want to go to.
Now because you are wanting a Wayfarer none of those stations really apply to you so click a random station it doesn't really matter which one, and then on the payment screen it will give you an option to get a promise to pay ticket.
Press that and one will print off.
Exchange that for your Wayfarer at the earliest opportunity, whether that is from the guard or from a gateline.
Note that this only applies to penalty fare areas, if where you are starting your journey is not in the Penalty Fare area and does not have a open ticket office, simply jump on the train and pay again at the earliest opportunity.
Sam