you could buy a smallhd dp4 field monitor and it has all the crop mark guides u will need instead of putting tape on ur cam http://www.smallhd.com/Products/DP4.html
Or for $549.98 cheaper you can print out widescreen bars on a piece of paper and looking at the viewfinder, mark where it should be.
I think older versions of ML have custom widescreen markers too.
an old school method for this was to use scotch tape (AKA magic tape). what you wanna do is fine the maths behind the the aspect ratio you want. measure out your screen. figure out where the lines wanna be and stick your tape down. this way your gonna be able to both see through the tape and clearly see where the frame lines are. this is what i do.