In a food processor, combine the cream cheese, sour cream, heavy cream, lemon juice, mustard, salt, and cayenne and process until smooth.
Add the ham and process until smooth. Scrape down the sides of the bowl, add the green onions and thyme and process until smooth.
Adjust the seasoning, to taste.
Transfer the mousse to a pastry bag fitted with a plain tip and refrigerate until ready to pipe into the gougeres. (Will keep refrigerated for 24 hours.)
Yield: about 2 cups