You can save a few steps by using Mesh > Transform > Shear instead of using the Knife Project. Select all of the edges you want at the 45 degree angle, select Shear then hit x or y (depending on the orientation of the mesh) and then hit -1 or 1 depending on which direction you want it to angle. The shear function also has one of those handy 10 finger hot key configurations. ;) Anyway, I hope you find it as useful as I do.