We have a main trunk branch and various other feature and personal branches in a bazaar repostiry. We'd like to keep personal branches in sync with the main trunk but allow each developer to remotely call 'pull' on his remote branch so that the remote is in sync with trunk. The developer then branches his personal branch to his machine, edits, commits (or branches additional branches as needed) and then can push the updates to his personal branch, or if the remote branch has updated - merge it (and thus latest trunk) with his working local branch before he pushes that up.
Later on a gatekeeper can pull the personal branches and merge them into the main trunk.
How can I issue such a remote pull request so that the remote branch pulls from trunk?
I think the step of pulling from the trunk to remote user branches is simply pointless.
In any case the pull operation is defined only for local branches. Triggering a pull in a remote branch would mean ssh server bzr pull -d path/to/branch, in other words you always need shell access (local or remote) to the branch you want to pull to.
Pulling to remote user branches seems pointless because the users could pull directly to their local branches instead. Your setup could be reworked like this:
Have a main trunk branch and various other feature and personal branches in a bazaar repository. The developer then branches from trunk to his machine, edits, commits (or branches additional branches as needed) and then can push the branch to his personal remote branch. Later on a gatekeeper can pull the personal branches and merge them into the main trunk.
At any point, the developers could merge from the trunk to get new changes that have been merged by the gatekeeper since they started working in their local branches.
Comment if you think this would not accomplish the same.
If you really want to update remote branches without shell access, push is the only way. You could do an automated push on all remote personal branches triggered by new revisions in the trunk, but as explained above it would be pointless. If the users want to sync from the trunk, they should just sync from the trunk.