Merge two Branches and version history

System

We have two Branches that are starting to share the same content (attachements) and it would be easier to merge the two Branches. I am looking to have all the version history of both Branches together in one.

I though about creating a new Branch and doing a copyTo but the old version history is still on the other two Branches and deleting those two after creating the new one would delete all the history.

Can a merge of two Branches be done?