I had a couple of ugly failed attempts - I won't bore you with the details or the ugly pictures - but I'm quite happy with this result.
This is the Chocolate Cookie Heaven recipe I've used before - http://affectioknit.blogspot.com/2007/01/chocolate-chip-cookie-heaven-man-cub.html
They held their shape well and melted in the cookies:
1 - 2 oz block of unsweetened chocolate - Nestle's is vegan
3 T of canola oil
1/2 cup powdered sugar
Melt the chocolate and add the oil and stir in the powdered sugar - that's all there is to it - then I put it in my cake decorator and piped little chips onto wax paper.