I have (kind of) done this:
https://bugs.launchpad.net/calibre/+bug/806939
The scheduler.xml work around is certainly something that would be easy to implement.
My only concern, would newer versions of Calibre possibly produce a different structure in the scheduler.xml file, so that when I used my old file months later would it cause a wobbly and/or errors.....
Suppose only testing will answer that! (But I'd probably be sitting by the pool at that stage
)