Recurly - Update Billing Details Form with ability to bypass login

I do not have an sql database for my site, I push my new customer signups straight into recurly via the recurly APIv2.

My customers do not require access to account management functions, except for when they need to update their billing details.

I am looking to create a form which enables my existing customers to do this (I prefer not to use the hosted account management) - and I do not want customers to have to login to be able to submit this form.

Therefore, my question is whether it is possible to create a link to be sent to all customers in the recurly email templates which directs them to the form where they can update their billing details (only push new billing details, not get existing billing details)?

So far, the best I've come up with is to somehow copy the unique account_code of the customer, and somehow push it to the form so that it can be pushed to recurly via the API.

Do you know if this is possible? Can you advise of a better method?

Thanks for your help.