Split the internal messages in a Queue destination in two - messages accessed by the PendingMessageCursor and work in progress or pagedInMessages - which are instances of QueueMessageReference - hence keeping the semantics for Message Groups etc. and keeping the majority of the 'fiddly bits' intact.
incubator/activemq/trunk/activemq-core/src/main/java/org/apache/activemq/broker/region/DurableTopicSubscription.java