That seems like an awkward "solution" to something that isn't really a problem.
It would be much less trouble to do as others have suggested and just:
1. Plug in either device.
2. Tell iTunes to "Sync selected playlists" and then check the box beside the ones you want. (You will probably want to create new playlists or smart playlists for each device, but obviously you'd end up doing that anyway, much less conveniently, in separate user accounts.)
3. Go to the Apps tab and check the boxes for the apps you want on that device.
4. Plug in the other device and do the same thing.
Now you're set. You can do this for as many devices as you want. Right now I've got two iPads and one iPod synced to one Mac using the same user account. No problem. It's how the system is designed to work. There is no "issue" here for Apple to deal with.