When I first tried the Simple Shower I liked the flow very much but thought I'd prefer a supply bottle with a handle.
It turns out a Coke bottle's threads fit very nicely through the cap of a standard 1-gallon water jug.
1- Cut off the Coke bottle just below the extrusion (in the photo, the blue ring is sitting on the extrusion I'm referring to)
2- Cut out the center of the jug cap. Trim away the lip on the internal side of the cap so the extrusion fits flat against the inside of the cap. You might also want to sand the bottom of the extrusion down and perhaps the top of the jug.
3- Push the cut-off Coke bottle threads through the cap and screw the assembly onto the jug. Check fit.
Note-
This solution is not bombproof. The thickness of the extrusion prevents the jug cap from using the full extent of its threads. There may be a better solution for long-term use.