I'm a bit late, but for the purpose of the opening post, I'd use sophomore geometry and a compass that reaches at least 2/3 across the sled to layout the lines - the wider the compass, the more accurate the results. First decide where on your fence you want to measure the 45 from; Then bisect the 180 angle at that point (which makes a line precisely square to the fence and two 90 deg angles). Now bisect whichever 90 deg angle you want to turn it into two 45s. That's your line.
There's lots of youtube vids on how to bisect angles, and it's super-simple. Only hard part is finding a compass with a long awl end, so the fence itself isn't in the way of the little bells and and whistles on some compasses.