As a contribution to technology and the development community, we have released an add-on that supports continuous Bamboo integration.
Our Bamboo add-on makes it possible to automate plan branch creation for pull requests, thus providing continuous integration with shadow merge commit builds.

The add-on provides build visualization after merging a branch upon a pull request. A branch planned for integration is targeted to a shadow merger commit branch (refs/pull-requests/{id}/merge) and waits for an update from the standard Bamboo polling trigger. A result build status is then automatically posted to the Bitbucket Server where it is available for display and use for veto management by the add-on.

Use CI practices on the shadow merge commit

Use the add-on to run continuous integration builds and verify the code for a target branch after the real pull-request merge. Bitbucket automatically rebuilds commits in case of any changes to the source or target branches.

Enable shadow merge commit builds

While creating or editing a build plan, you can automatically create plan branches upon pull request creation to build a shadow merge commit (refs/pull-requests/{id}/merge).

Shadow merge commit builds run automatically

Each pull-request creation and event update is automatically followed by the next branch build with its status posted to the Bitbucket Serve.

You can find Shadow merge branch creator for the Bamboo Server here.