Although I have done the "clamp it securely and raise the blade into it" technique before, I would not recommend it to anyone else for the same reasons as my friends above - safety is questionable.
-> Just because "x" of us have done it without injury, there is no guarantee that it will work out safely for whoever tries to be "x+1".
My objection to using a saw with a circular blade (table saw, miter saw, plunge saw, etc.) is the shape of the resulting non-through slot due to the curved blade. Perhaps it is not a concern for Cody (@Ivegotwood69). It would be a concern for me.
Another concern with miter and plunge saws is that they will require multiple cuts to achieve a shelf-width slot. That compounds the difficulty and the risk. I have never seen one of those saws with a dado-type blade.
That's why I suggested a plunge router, provided the angle and depth can be supported. With a router, Cody will need an angle jig of some kind. In addition, he will need to square up the corners, but the non-through slot should be perfect. Again, without knowing the angle and slot depth, it is hard to know whether a router will work.