Signing up is really easy in StumbleUpon. Just click on the button "Connect with Facebook" ot "Connect with Google" and you are in. No worries, it won't post anything.
If you don't like signing up like this you can manally enter your email, username, password etc. as well.
It costs you just a minute, so you have nothing to loose. After publishing a post just add it to stumbleupon and the next day you can check on google analytics how many users came from stumbleupon.