Not a popular option, but an option nonetheless: Change your last name to match that of your child.
That aside, have a read here: http://courts.mi.gov/Self-help/cente...eChangeSH.aspx
You may need to look at your current state's laws, too. Google is your friend
(Given that the child has never had Dad's name, you shouldn't actually have too much trouble changing the last name - although doing so outside of a stepparent adoption is often referred to as a "backdoor adoption")

