How do I setup AWS so my users can use a 3rd-party "custom domain" to point to my AWS ELB application

Hi Beau,

You can register a new domain [1] or import an existing 3rd party domain into Route 53 and route the traffic to your Application Load Balancer [2].
A guide on getting a new domain to route traffic to your load balancer can be found here: [3].
An example of how you can integrate 3rd party domain name with route 53 for your website can be found on this blog [4].

References:
[1] https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/domain-register.html
[2] https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/routing-to-elb-load-balancer.html
[3] https://aws.amazon.com/getting-started/hands-on/get-a-domain/
[4] https://medium.com/weekly-webtips/how-to-integrate-3rd-party-domain-names-with-aws-route-53-for-your-website-webapp-7f6cd8ff36b6

Regards,
Atul