If you create a second admin user, then the primary (built-in) admin will be bumped from the welcome screen. It's probably best to have two admin user accounts on a machine anyway. If an install procedure borks your one-and-only admin account then things can get kind of tough. But if you're just not wanting to have ANY admin level user show up on the welcome screen, I'm not sure whether or not that can be done.
- Collin