Yes, it is most definitely possible.
I actually did this myself last week.
If you are missing under 4 days (which you are), you use this:
http://www.mcmaster.ca/msaf/
click "I agree", sign in and follow the simple instructions.
All you have to do put which class it's for, what it is (midterm, etc), how much it's worth, the date you're missing (Friday), the professor's email, and what the reason for missing it is. It gives you 4 options: illness, injury, personal reasons, religious reasons. If it IS for illness, you don't need a note or anything, either. That's the beauty/simplicity of it.
You can only use this form twice a term, though. I'm not sure if you'd be able to fill it out NOW or if you'd have to wait til the date is closer (I filled out mine the night before my midterm), but you can definitelyy try doing it now and if the date of your midterm isn't listed as an option, try again tomorroww.
What I did after that was send my prof an email sort of explaining the situation and he had my final exam weight readjusted accordingly.