Your sled and it's fences can span your saw table and a 45° cut through the front and back fence will help with accuracy. A solid block, like 3" thick, should be glued to the back of the back fence, spanning the cut line, for safety. Both fences should be at least tall enough to allow for manipulating the sled and still keep the fingers safe.
I use two miter slot runners and generous wax under my sled.