Bad news ... you can't hide them, sorry!
However, you can lock them so that your customer will not be able to use them. Create a script which includes the "Set Zoom Level" - set it to 100% ( or whatever you'd like it to be ) and remember to check the "Lock" option.
Just remember to have a script to unlock it again when you work with your solution ;-)
Thanks for the bad news:( At least I know...
What's up with Filemaker Inc. to leave something like this when everything else in the interface (menus, buttons, etc) can be changed. Someone who has the ear of their dev team should tell them what I'm sure a whole lot of us believe, that they should provide a way for us developers to control this.
There is a suggestion form where you can request a new feature: http://www.filemaker.com/company/feature_request.html
You can also post the same information to the Feed Back forum--that may prompt other forum members to also post the request--which might give it a bit more impact. TSGal suggests including a "real world example" of why the new feature would help you. That sounds to me like a good way to make the suggestion more persuasive.