If using a fence with a bearing bit, you can use a straight edge to span the split in the fence, the move it until the straight edge just touches the bearing. If you are cutting stock for a frame and it is cut to length and/or you are routing after cutting the miters, this technique will reduce the chances of tear out. For this reason I usually route before cutting the miter with a little big longer piece than needed, then final cut the miter to exact dimension. I generally allow an extra bit of more width and length on the rabbet than the size of the canvas.
When routing the face of the frame with a longer, vertically oriented bit, I cut in one pass and finish with sanding with a shaped block. I start with a piece that is much longer than required and make passes so there is a bit of flat at the ends, this is particularly important if you are going to use multiple bits to shape the frame front. A long fence is required for this if your frame is fairly large.
My wife is an artist so I make a fair number of frames. It's far cheaper to shape your own material than to buy it, and I find that a LOT of frame stock is too warped to use, so you wind up with a lot of useless, costly scrap. It's much cheaper to buy shorter chunks of wider stock, prep and cut it into strips and mill those on your table. Even then, it's a good idea to do it all on one day because warping can happen very fast.
Here is a picture of the sanding blocks I got from Rockler. I use the 3M flexible sanding material with them and can final sand up to about 220 grit in minutes. There are straight and wedge shaped blocks as well. I think I paid less than $12 for them, and the different sizes seem to fit every curve perfectly.
The more I do, the less I accomplish.