That's the method I prefer aswell - Thanks for the link ZeissFan, the pictures are a lot clearer than my explanation above.
I used my Hasselblad with the waist level finder and the magnifier - worked perfect for infinity targeting.
Now is there a similar easy way to confirm if the intermediate distances (eg. 3', 5', 10' etc...) are also spot on? I tried the same approach by setting the focus on my Hassy at 10' and seeing if the rangefinder targeted at that, but it was just a blur in the viewfinder.