Upon Render Remove Countries From DropDown List

Hi, I have a dropdown list of countries used to select which countries I'll ship to.
I really only need it to be United States and Canada…. but the list of options includes about every country there is.
I cannot alter this list, there is a template tag that simply spits out the following code when the page renders (list shorted for ease of display)
<select name="billing_country" onchange="document.billing.action='checkout3.asp?step=3&amp;action=updatecountry';document.billing.submit();"…
Upon Render Remove Countries From DropDown List

See original post by theblade24