I did come across those in my search and wasn't sure if they would work out of the box for this application, do they do look handy as heck for a myriad of things. Might get one just to have.How about something like a Quick Spade?
Paumco Equipment | Quick Spade
I've done shallow trenches by cutting with a middle buster and then clearing the soil out with a trenching shovel. Once the soil is broken it's pretty easy.