I've got a prototype I've been working on - nothing really extraordinary in terms of materials though.
I've not written the pattern up for my site yet, but I've got a couple of pics.
Basically its a closed cell foam underbody, red glass/plastic bead and melanistic/dyed pheasant tail 'shellback' and legs.
I intended it to float, for those days when smallwater trout are bulging just under the surface and just aren't interested in emergers... however, what I seem to have achieved is a very slow sink, which seems to work nicely all the same.
The proportions still need some work - not very practiced with foam yet - as corixa are fairly flat bodied instead of rounded as my fly seems to be. I've found a couple of ways to achieve it using 2 pieces of foam, but it trebles the tying time and I'm a big fan of simple to tie flies.