Low competition, high traffic keywords - how can they help?

I've identified some super high traffic keywords in my market with zero competition, but I don't know what to do with them or how to make them help my site grow.

For the sake of this post, let's say I'm a plumber, and I am already have an authority site for local searches. Now let's say I want to add content to the site. And I have a silo architecture like so:

PlumbingSite.com
Locations We Serve
Brentwood Plumber
Los Angeles Plumber
Hollywood Plumber
etc
Resources for plumbers (THE NEW SECTION I AM BUILDING)
How to become a plumber
How to replace a toilet
How to maintain a septic system
etc

Now, let's say I discovered that the "how to become a plumber" search phrase has tens of thousands of searches a day but zero competition and I can easily rank first for that.

The problem is that the site visitors for that term aren't going to be clients. But, I am already an authority site on plumbing and can rank for that term.

I am looking for creative ways to get get the how-to-become-a-plumber.html page to directly help my site rank better for hollywood plumber and my other related search terms, which is where I make my money.

What are some effective methods for this?