Looks like it sorta is in the registry, but if WMI is in place, the following WMI query will shake it loose:
wmic service where "name Like '%SQL%'" get Name , StartName
Found the query on Stack Overflow at the following site:
http://stackoverflow.com/questions/7324407/get-service-account-details-of-the-sql-agent-service
Enjoy...
Steve (aka sgmunson) 🙂 🙂 🙂
Rent Servers for Income (picks and shovels strategy)