Ok Lenny, I have just experimented, taken granular erythritol and put it into the coffeemill, left it running until it almost overheated, perfect icing sugar substitute.
I made peppermint creams, use a measuring jug = 100ml powdered sugar, 2tbspb double cream, 4 drops of peppermint essence, the mixture is quite soft, but you can work with it, if you prefer leave it to stand a little longer to firm up, but they hold the shape well, chocolate covering is just drying as we speak.
So you can use your erythritol after all, actually the erythritol leaves a slightly cool taste so it kind of accentuates the mint flavour.
On an American site someone recommended a powdered sugar subsitute using Splenda.
Blend together until you have a very fine powder:
3/4 c. Splenda granular
2 T. cornstarch
(yields about 1/2 cup)
1 T = 5 carbs