Adding web sockets to project with custom domain

I’ve got a project that uses web sockets, and I’d like to add a custom domain. Glitch’s help site says:

Currently, web socket connections do not work with custom domains on Glitch. If your Glitch projects use custom domains and web sockets, you will need to set them up so that the apps are connected via their glitch.me URL.

What does this mean? How can I connect my custom domain site to its Glitch version? Is there a way I can have a site with both web sockets and a custom domain?

Thanks in advance.