I have run transactional replication in the past where I have customised the replication stored procedures in order to preserve data at the subscriber. I've never done much with merge replication though so I don't know if this would be a viable option. Do you need to use merge replication in this scenario or would it be possible to use transactional replication with an updateable subscription?

Sorry I don't have any exact resolution but if no one else has a quick answer I'll be more than happy to tinker with some scenarios and see if I can come up with anything:-)