I've marketed that when I was actively working..... Custom builder will build on your lot with your plan or his.... write blog posts.... mail postcards to owners of lots.... he could go partners with a land owner.... establish a price for the lot.... find a buyer for a custom home on that lot... and you have a deal....

Barbara Todaro has the best answers and she is always a good person to ask!

Justin Arlequin I am sure Barbara Todaro will have an answer on this.

Some good ideas in other answers, too. Good Luck.

 Where is Barbara Todaro?  She will have the answer.

Barbara Todaro  has your answer, no need to expand on it. 

In this case, I would go directly to the agents (perhaps via permission to attend an office meeting?) and let them know that if they have clients purchasing a lot with the intent to hire a builder, working with your builder would provide commission - and make sure your builder will do this! Have a formal agreement how this would work - say 20% of commission at contract signing, 40% after framing, and the balance at completion. We have builders in the area offering these incentives for agents to recommend them to clients. 

Barbara Todaro nailed this one!

I am sure Barbara Todaro will have some insight on this as will Mike Rock 

Spread the word to other agents as they have the buyers that will need the services. You can work together on it.

 I would get a commission from said builder for selling his custom homes no matter what lot they put it on. ...

Have never sold land. The best person to ask is Barbara Todaro. 

I would have a one to one phone call with Barbara Todaro and pick her past knowledge on the suggest.

As Barbara Todaro Wrote. Patience and diligence is the key!

See what Barbara Todaro says... she's got experience here.

The guru of marketing builders Barbara Todaro has the answer!

It should be coordinated with a model home.

I think what you put in your title says it all and would be a good place to start. 

Others have answered.

Most buyers want to choose their own builder first. Then they look for a lot. There are many builders that will build on any lot even though they might not advertise that. Talk to a few builders, and see how they work. I have one that offers 2% on the base price sale amount. Add that to whatever you get for the lot sale if you list it or represent the buyer on the lot.

If your target are buyers, blogging, and print ads can be effective.

For Realtors, direct contact with email follow-up!

"Best way" depends on the specific target market.

I have seen custom builders develop connections with listing agents of land in certain areas.

Mail outs, blog posts, advertisiments - lots of ways to get results

I think, it also depends on the location, but online marketing can give you unlimited exposure, so it is up to  time you want to invest and your budget. 

Pictures of homes on other lots?  

Market to lot owners.