[Moo] Can we load MooTools after the page is finished loading?

[pradador]

Let's say I'm on a page and want to use MooTools after the page is
done loading for whatever reason. Is it ok to load the MooTools script
dynamically at that point by injecting a script element into the head
of the document? I tried doing it via the Google AJAX library api and
got a "Must be done before DOMload" error or something like so I
thought I'd ask why that is.