I-130 After Marrying on a Visitor Visa

Now I understand it is not the preferred method due to it being high risk, but if someone were to marry while visiting on the VWP and then file the I-130 & I-485 together, how would you answer the question about your I-94 #, since this is now done electronically through ESTA?

Thanks for your help in advance.

If you entered and were approved without the issuance of an I-94, your ESTA approval replaces the I-94W form. You can answer "None", "N/A", or if you want to be more clear about what happened, "VWP/ESTA".

(For anybody else coming along, if you were issued an I-94 and have lost it, you can order a replacement with Form I-102.)