wait is this a plugin or are you requesting this for a plugin and is this a creature made of blocks EDIT by Moderator: merged posts, please use the edit button instead of double posting.
Yes. The only problem with using pistons is that Notch blocks pumpkins from being pushed. I don't know if thats possible to fix with a plugin or not. My method saves a lot of space, and keeps Notch's original intent for pumpkins being 'fragile'.
I think it could be done! If there is a Pumpkin entity on the ground. Check if there is snow under it. And under that block to. If there is snow under it. Remove that pumpkin entity and place a pumpkin on top of it. Which will auto create a Snow Golem.