Hi CF_Pro,
I believe the best way to accomplish additional addresses in Method would be to use Jobs/Sub Customers. By setting it up this way, you can have additonal addresses linked to the original Customer, and all info will sync between QuickBooks and Method. This can be done by creating a New Customer, once you have filed this information out, check off the "Additional Info" checkbox for more options. Depending on which version of Method you sync wtih, you will see a dropdown for "Job of Customer" (QBD), or a checkbox for "This customer is a sub-customer?", then a dropdown will come up, listing your existing Customers to link with (QBO). I hope this helps.
-Ben