Scripting a Maintenance Plan in SQL Server Express
You've pretty much self answered here - you won't be able to rely on SQL Server to do the scheduling for you. 

The most common method is to use Windows Task Scheduler, but if you have any other job scheduling application already that might be a better choice. Either way, you'll need to get comfortable with the sqlcmd utility if you aren't yet. 

If I were to use Task Scheduler, I would personally chain any dependencies together in .bat files, assuming your maintenance needs are fairly simple since its an Express instance. 

I've got a website post with all of the specific steps to setting up Ola on Task Scheduler if that is the route you decide to pursue. There is also a Microsoft KB with similar (though pictureless) instructions.