SvelteKit: How to specify port number on node build?

I'm trying to develop a series of SvelteKit apps for my business. I want to run them all on the same Windows Server using Node; they're fairly small.

I can deploy the first one (using the SvelteKit Node adapter) fine on port 3000. However, the next app I build & try to deploy wants port 3000 as well, and naturally I get a Error: listen EADDRINUSE: address already in use 0.0.0.0:3000 error. I can use port 4000 for app #2, 5000 for app #3, etc. This is pretty easy to setup using host headers in IIS & URL Rewrite. However, I cannot find a way to declare a specific port anywhere.

My question: How do I specify the port I'd like to serve each SvelteKit project on?

I've seen a few posts & blogs on this... Here's what I've tried:

• Creating a .env file at the project root with CUSTOM_PORT=4000& a envPrefix: 'CUSTOM_' directive in the adapter() in svelte.config.js. This simply gets ignored.

• Starting the build with PORT=4000 node build. This results in an error: The term 'CUSTOM_PORT=4000' is not recognized as the name of a cmdlet, function, script file, or operable program.

• I've tried variations like node build PORT=4000, node build --PORT=4000, etc. All produce the EADDRINUSE error.