Eu resolvi isso introduzindo isso no console:
var script1 = document.createElement("script");
var script2 = document.createElement("script");
var head = document.querySelector("head");
var text = 'myscript();';
script2[(script2.innerText===undefined?"textContent":"innerText")] = text;
script1.setAttribute("src", "http://mysite.myscript.js");
head.appendChild(script1);
script1.onload = function(){ head.appendChild(script2) };