To bulk upload or add multiple environment variables to Vercel's dashboard or CLI, users can leverage the bash shell, jq, and Vercel CLI by defining environment variables in JSON format, transforming it into vercel env add commands using jq, installing jq and the Vercel CLI, linking their application codebase locally, creating a JSON file for specific environments, specifying which environment to import, running the `vercel env add` command, deleting sensitive data files, and repeating the process for other environments.