gold card discount on oyster card

[Skimpot flyer]

Quick query...
Where is the best London station (preferably a GN station) to get my Gold Card discount loaded onto my Oyster Card ?
I have a Lapworth - Hatton annual season but stupidly forgot to have the Gold Card discount added at the time of purchase !
Last year, I think I went to the (then) First Capital Connect window at Finsbury Park, but I don't normally use the station for anything other than interchange to the Victoria Line. Can I reach the ticket office without going through the gateline? If not, I'll have to purchase a ticket tomorrow on which break of journey on the outward leg is permitted, in order to re-enter the station after getting my Oyster updated.

Thanks in advance

 

[TCDD]

I got my (Ryde) Gold Card discount added no problem at all by a member of staff at the Underground 'ticket hall' at Waterloo yesterday. He logged into a special function on the self-serve ticket machine and it was all over in seconds!

 

[Hadders]

Kings Cross St Pancras Underground Station sorted my Oyster discount for me last week. Saw a member of staff who was supervising the ticket machines in the tube ticket hall and he sorted it in a couple of seconds. I was impressed.

 

[MarlowDonkey]

Kings Cross St Pancras Underground Station sorted my Oyster discount for me last week.

I've recently used Paddington Underground to load a Senior Railcard to Oyster. There's usually a member of staff somewhere close by to the ticket machines who knows which keys to press.

 

[Skimpot flyer]

UPDATE: I got the Gold Card discount loaded at Finsbury Park last week, it took less than a minute