There is no Revit API / official supported method to do this, but using some unnofficial hacks related to Autodesk.Windows.RibbonControl can most likely achieve what you are after.
I have a question though, why would frequent synching be a problem? A better solution might be to catch the synch events in the API and ask the user to confirm the action after explaining the issue using a task dialog. This will allow the user to perform the synch if thye feel that it is indeed important at that time while detering overuse of the command. You could even use a timer to only show the dialog if synch has been called within say 5 min of the last time to reduce impact on users that are already doing the right thing.
Blanket banning the Manage tab / synch to central command seems a bit heavy handed to me, especially if the user wishes to use Revit to do something else like create a family or prototype an idea seperate from the central model.
