Restart on dependency respawn

Hi,

Suppose I have service A and B. I'd like upstart to do the following:

1. Start A when B is about to be started.
2. Restart B when A gets restarted (or respawns).

The first requirement can be easily achieved by "start on starting B" in A.conf. The second one is a problem though. If I put the following in B.conf:

stop on stopping A
start on started A

it will basically do the job, however I will get two unwanted results:

1. B will be stopped when I manually stop A (while I want to just stop A, leaving B still running).
2. When I just want to start A, B will be started as well.

How to solve this problem? Thanks for any help.