I'm looking to do the travel for a tenner Ponte And Cas newspaper promotion tomorrow but I start my journey at an unstaffed station.
Presumably the conductor on board can't do the relevant ticket so is it a case of telling them you'll buy the ticket at the first opportunity (first staffed station)?
Officially you have to get the ticket from a staffed station on the Northern Rail network, or discuss your options with the customer service team, before you travel.
Unofficially, if you ask very nicely and make it clear what you intend to do, some guards may simply let you travel so you can buy your ticket at the first staffed station you change trains at. I am also led to believe that the Avantix (portable ticket machines guards carry) have now been programmed to sell the £10 day rangers, so again if you ask very nicely you may be able to purchase one on board (again albeit unofficially).
Here is another forum member's experience:
I was surprised to find that onboard conductors are now able to issue these Day Ranger tickets from their machines.
I travel from Bamber Bridge to Preston where I normally purchase my ticket by handing in the form and tokens. Each time previously I have asked the guard before boarding at BMB if I'm okay to travel free to Preston where I purchase my ticket. Luckily I've always been allowed to do this and save the £3.20 that I would normally have to spend.
This time I showed the guard my form and he was unsure what my form was but agreed to allow me to travel. Before arriving at Preston he kindly returned to me and said I've found your ticket, you don't need to queue at the ticket office now. I was impressed and thanked him for the effort. It also made it easier in passing the Northern RPIs on the overbridge at Preston. I also got to keep the form as he said he didn't need it. I was told I could reuse the tokens! Bonus.
Of course just because some others have had success with these unofficial options does not guarantee that you will be equally successful, but is worth a try.
If all else fails then just buy a separate ticket to your nearest staffed station.