Yes, there are other ways of starting apps on Windows at boot time other than via a service. But why do you want to use a mechanism whereby you need to first understand the Windows boot process, make manually changes to registry entries, and fix all of the issues yourself instead of using a simple BAT file that is already provided that can set up a service for you?
By the way, if your answer is that you don't have admin privileges on the system, then THERE IS NO MECHANISM whereby you can start the app server on boot as they all require admin privileges to set up. (You could place a shortcut into the "Startup" folder such that JBoss AS runs when you sign in, but note that this happens during login and not during system boot.)
If your hesitation is regarding running the app service with the SYSTEM account, then you can easily create a limited user account to run JBoss AS. In fact,
you should do that anyway.