I found a good solution: Use a URL that automatically runs a javascript something like the following code:
<!DOCTYPE html>
<html>
<script type="text/javascript">
function autoEmail()
{
location.href = "mailto:you@example.com?subject=Data&Body=Verification Code: " +(new Date().getTime());
window.onload = autoEmail;
</script>
</html>
This'll automatically open up the default mail app, and will place a timestamp in the mail. This will always be a unique code, and if you want to randomize it you can encrypt it or perform any of many operations on it.