Obviously an FSM baptismal is just as "valid" as any other religion's baptismal - but something tells me you'll have an uphill fight on this one. You might want to take a look at a bunch of baptismal certificates from the "mainstream" churches and make yours a little more formal looking if you want to avoid a lot of hassle.
Here's a bunch: Bing Image Search for Baptismal Certificate
Of course, if you're like me, you might want
the altercation to prove the point, but if you simply want to get your daughter registered for class, maybe tweak it a little.
Also, I could see where they may not be too keen on you being the one certifying to the baptismal as you obviously have a potential incentive to lie (since you're a related party). I know that in Florida, our Notaries Public cannot notarize any document for anything that they have any connection to - to avoid such conflict. Perhaps another friend or family member becoming ordained and attesting to the baptismal may be more effective (if such is practicable).
Very interested to hear how this goes - please do keep us posted.
I can see the fnords.