What are the allowed values for commandName in a launchSettings.json profile?

I am trying to set up a custom launchSettings.json profile that runs the executable specified by the executablePath and commandLineArgs arguments.

However, it requires me to pick a value for commandName in order for F5 to work. IIS and Project both work but they seem to do the conventional things.

• What other options of commandName are available?
• Is there another way to build a fully custom profile?

    {
        "profiles": {
            "Custom": {
                "commandName": // what should this be?,
                "executablePath": "mycustomexecutable.exe",
                "commandLineArgs": "my custom args"
            }
        }
    }

UPDATE: it seems that another option is "executable", but this causes VS to try and debug that executable. In my case I want to run a shell executable which will perform some setup and then ask VS to attach to the currently-running process.