Step 1: Attach Flash Stand
Drill a hole through the stand and bolt in to place through one of the holes in the base of the lightshade.
I happened to find a hollow black plastic tube that acts as a spacer, but it's not totally necessary.
Step 2: Prepare Diffuser
Measure your flash head and cut an "H" shape in the lid to allow the flash head to push through.
Step 3: Cut Hole in Lightshade
Drill 10mm holes at each end.
Cut two more slots to make an "H" shape that's about the same size as the one you cut in to the diffuser.
Once cut, place the diffuser lid inside the light shade and bend the metal "flaps" through the diffuser lid's flaps to secure it in place.
Reattach the tupperware diffuser to the lid.
Step 4: Insert Flash and Mount on to Tripod
I inserted my flash upside down to keep it out of the way and help with balance.
Step 5: Results
I might put a black card disk in the bottom of the diffuser to reduce direct forward light, relying more on the bounced flash - not really used this rig in anger yet, so I'll post comments if I find any significant improvements through use.