Additional Information box in Cust A/c & Checkout

Hi

I am not sure where to ask this question, so I hope it's ok in here.

When I ship products, my customers must tell me where I can leave their parcels if no-one is in for the carrier when they deliver the parcel.

I would like to have a box where they can tell me this either attached to their address book, in the checkout area, or somewhere else in their 'account' on my site. I don't want them to have to keep putting the same information in every time they shop, so want it to 'stick' on their account unless they want it to change.

I know there is a comments box on check-out, but my products are such, that I mainly get repeat business, so I don't want to hassle them with the same information every time they return obviously, but I do need these details.

Is there an add-on for this that I haven't spotted?
It is easy to configure for someone who isn't a programmer, but can do a little bit of configuration?
Or do I want to hire a 'zen programmer' to do this for me?

Thanks

Paul