Add "ask for invoice" during checkout

[peorthyr]

Good day all.

My idea is quite simple, I'd like to ask to the user if he need to have the invoice, I'd like to ask him BEFORE he enter the addresses because I have t check if the address has the required information for invoicing.

I'm struck in searching for the right hook to use in the module, seems that the nearest is "actionValidateCustomerAddressForm" but I'd like to ask for it "BEFORE" and not during the address validation (if you know what I mean).

can you help me pointing in the right direction... is maybe worth to look for a controller override instead?

thanks in advance.

[peorthyr]

Actually I manage to inject te question just before the "payments"

but I'm struck on "how to save a field value". I mean, I'm on the payment step, I put there a checkbox, now, I'd like to save the checkbox state (if it's checked or not), once the user go ahead with the checkout...