I think you might still be able to do that with that widget! It looks like the widget exports a function you can call to convert new p5 script tags into editors. So you can add the exported code to your page by doing this:
const scriptTag = document.createElement('script')
scriptTag.setAttribute('type', 'text/p5')
scriptTag.innerHTML = yourSourceCodeHere
document.body.appendChild(scriptTag)
// Turn the tag into an editor widget:
window.p5Widget.replaceScript(scriptTag)