Instead of using cement board on the threshold, pre-form a sleeve of galvanized expanded metal by bending it over 2x4s. Pinch the legs of the metal in slightly so that the folded metal grabs the threshold.
Hold the wire 1 1/2 inches off the bottom of the shower pan, with the factory edge (without sharp edges that could puncture the membrane) on the inside of the pan.
To keep the weep holes in the drain clear, spread a small amount of pea stone around the base of the drain.
Dump several buckets of dry-pack mortar (the same mix that was used to create the sloped layer) onto the membrane.
Pack the mortar tight to the membrane, especially in the corners, along the perimeter of the shower, and around the drain. Smooth the mixture using a wood float and a steel floating trowel.