Update : April 2019
Bitbucket Server and Data Center release 5.6 includes some changes to make it easier to find your own personal forks, as well as any other forks of a repository.
Original request description
I've created a pull request, which is quite large. And therefor the approvers might wanna clone it to test it.
I've then given the approvers read and write permissions to the fork, so they can test it.
But they are unable to find my fork via the UI. The only way is to know the URL.
This problem makes this feature a lot less usable