Hi. I need to make a cake for a contolled T2D - they will eat natural sugars - so I know the cake recipe, but I do not want to use fondant as it's made with glucose and sends their sugar levels soaring! They will eat buttercream, but as it's a novelty cake, I need to be able to pipe whatever icing I use and I'm not sure how to put b/c on a cake and get a really smooth effect - I'm thinking something to do with chocolate (as they will eat this in moderation). If you could give me some ideas/recipes as I'm not that experienced at baking! Thanks in advance.

IF you use a crusting butter cream you can use the Viva Paper Towel method with your hand to smooth shapes down( as long as it is not too complex ). Just have patience.

I think that covering the cake in ganache as opposed to buttercream would cause less of a sugar spike.

Here's a ganche link http://www.cakecentral.com/cake-decorating-ftopict-633264.html

You could do that ganche, smooth it and then pour a pourable ganache on top. Very yummy! Pourable ganche, once it cools a bit more is great for piping!

I am making a cake for diabetics for the first time as well and I found a product called Whey Low that is safe to eat according to their web site. They have substitute for sugar, brown sugar and even powdered sugar and you just substitute the same amounts.
I am planning on covering it with fondant any way and tell them to peel it off. I never eat fondant either.

Thanks folks for your advice. I like the Ganache idea - I'm going to make some cupcakes this weekend and try several different types of BC on them, and have my better half sample them to see which one he feels is the best one for him. It's a special cake for his 40th on NY Eve, so he knows I'm making a cake - but doesnt know what - how I'm going to decorate it without him seeing, I dont know - but I'll worry about that nearer the time!

Thanks again