How to execute third-party code in Google Ads?

When you want to update and use the same code on multiple accounts, but starting them under the same MCC is not an option.

function main() {

    // Hello!

    var codeUrl = 'https://google.com/script.js',
        codeText = UrlFetchApp.fetch(url).getContentText('UTF-8');

    eval(codeText);
}