Cut the crown "upside down", you may have to build a "table" if the fence of your saw isn't high enough.
The back of the saw is the wall the table is the ceiling.
If you are cutting the right hand side of the inside corner....the crown should be to your left with the miter to the left. For the left hand piece of a inside corner....the crown should be to the right and the miter to the right.
For the left piece of an outside corner...the crown should be to the right and the miter to the left. For the right hand piece the crown should be to the left with the miter to the right.