We do allow for the choice on a record-by-record basis. What we cannot allow yet is you changing it at runtime.

One way to implement the choice record by record is to implement formula fields. You'd have one editable field on your record called "Preferred Address" and it'd say "Billing" or Shipping". Then you'd have a formula field for each address component (street, city, state, zip, country) and output the billing or shipping address field based upon the Preferred Address selection.

Then Geopointe's Map Object would be setup to look at the formula fields.

If an Account has a Billable and Shipping Address, then allow the object to be mapped to either. If both addresses are present on an Account, then let user determine which takes priority (as a rule) or allow user to manually determine one-by-one.