Not only can I not think of a way to do it, I have never, in 15 years, seen an organization that successfully managed junior engineers in a way that resulted in the production of code on par with what senior engineers would produce.
Getting good work out of junior engineers requires a management investment greater than the cost of simply hiring experienced engineers to begin with, and they still will not produce code to the same level of robustness and quality.
I can see from your company that you don't operate this way. I assume this choice expands the apparent pool of available applicants, but it also ensures that your company is likely completely uninteresting to senior, experienced, genuinely expert engineers.
In my experience, there are two kinds of engineering managers. The first is the kind that has figured out (or thinks they've figured out) how to get decent enough code out of inexperienced or just plain bad engineers. The second is the kind that realizes that they don't have to work nearly so hard or jump through so many procedural hoops if they just hire people that know what they're doing to begin with.
What's more, those experienced people tend to have extensive contacts and make it easy to hire their friends.
That said, I'm happy to let you spend the time, money, and energy training and managing junior engineers, while dealing with their subpar work output.