As much as its not very useful and most likely a wee bit daft there is another option....ditch outlook and use
http://www.emclient.com, I am not affiliated with them at all but have been using it alot recently with customers who are too tight to buy office. It uses activesync I believe so should work fine!
The other option is to fork zentyal to a truly open source project which has all this available as part of it and don't do it to make money (which wont work).
I have been using zentyal since the ebox days and love it, in fact I had been building a similar project and abandoned it due to the fact that ebox was far superior and has always ticked so many boxes for so many of my customers both using the community and paid for versions.
With my business head on though realistically if outlook sync worked fine without a workaround in the community version then what would be the need to buy it?
Also putting on my community hat would a scheduled send and receive work? If so I believe the send and receive settings for outlook are kept in a srs file which will be stored in "C:\users\%username%\appdata\microsoft\outlook\" and will be called mailprofilename.srs, if this is the case that wouldn't take long or be awfully hard to script a deployment using pdqdeploy or logon scripts as the default outlook profile is always called outlook.