Hi Brian,
There is a long and short answer. First the short answer: No, it is not possible to convert a QBDL to group (SmartDL or otherwise) without deleting the group and re-creating it.
Long answer: There is a special objectClass in AD called msExchDynamicDistributionList. A group has an objectClass of group. To migrate a QBDL to a SmartDL you would have to change the object class of the QBDL to group. There is no way to change the objectclass of an object in AD. You have to delete the QBDL and create a group. Even if SmartDL supported upgrading a QBDL to SDL, it would basically have to do the same thing: delete the QBDL and create a group with all the same attributes, which would still break the Address Book.
Sorry :(
--Robert