redirect parent and child instance std out to a karaf.out file

When starting the root instance with bin/start, the std output is redirected in data/karaf.out.
Unfortunately, there is not way to redirect the std output of a child instance (bin/instance just delegate to the instance Karaf commands).
This limitation is fixed in karaf verson 3.0.3, 2.4.1, 4.0.0.M3
Please provide backport patch for this limitation.