The best way to do this is to implement a custom workflow (http://wiki.alfresco.com/wiki/WorkflowAdministration) where the first step looks at the content and branches based on the value of the "onFrontPage" attribute. The "true" branch would include a manual approval step, while the "false" branch would simply go directly to the promote-to-staging step of the workflow. So while there is still workflow for all content, that workflow is 100% automatic (no manual intervention required) in some cases.
One wrinkle is that you might need to think about how to handle the case where a user submits multiple items to workflow as a single change set. My thinking would be that you'd have to scan all of the content items in the payload of the workflow to see if any of them have the "onHomePage" flag set to true, but that's just a guess on my part as to your requirements. 😉