I'd contact Cannondale directly -- either via their web site's customer support or via Twitter @RideCannondale. The 'toppers' with 0 or 25mm offset might be your ticket to bike bliss... assuming we are interpreting correctly what the deal is.
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Okay kids - what was I thinking? Of course, the one thing that was being tightened was not a clamp on the seatpost, but a clamp that holds the saddle in place on the rails (forward, backward, angle). For a supposedly intelligent person, I sometimes manage to confuse things pretty well!
My DH tightened it again before riding today, and it seems to be holding itself level and in place after 32 miles.... hopefully it will stay there. I did not have a problem with the saddle moving forward or backward, just tilting.
Still- maybe someone can confirm that this really is okay to have the seatpost reversed 180 degrees like this. (It was when I rode over a substantial bump and came down a little harder than usual on the back of the saddle, that the whole problem came up.
I have never seen any warnings against reversing a seat post like you've done. In fact, it seems like this used to be a common way to "convert" a road bike into a tri-bike.
I specifically browsed through Specialized tech docs on seat posts, and I saw no warning against doing this. But if you want peace of mind, go to Specialized's web site, click on support, and choose the option to "contact a human now".
I actually stopped by a local Cannondale dealer (not MY dealer, cuz I loathe going there) and they let me browse through their 2012 dealer book. In the book, I read that the new seatpost IS compatible with 2009-2011 Synapse models. So yippee!!! I got my answer, and this dealer sent out an email to his C'dale rep inquiring on price and availability of the seatpost. He will contact me on Monday.