Can you give a quick outline of what you are thinking. I would love to try and write one. I am just not sure the steps or facilities of the add-in SDK that would help in such a case.
For example: start from the HexView add-in sample, replace AddIn_OpenDocument() with a call to CreateProcess for POIDE using the /x option, probably the /n option, and any filename. You start through the context menu, not a double-click, but maybe enough.
Note that pcvData will be NULL for the project target (xyz.EXE, xyz.DLL) in source file view - this works best from the target file view in the project tree (use button over the project tree...).
Pelle