The shell integrate thing that comes with 4nt does this for cmd files as well as btm files. I use it to run EXTPROC batches under cmd.exe shell.
You may look at
http://www.maddogsw.com/cmdutils/ , which has utilities for context and propsfor, which opens the context menu, and properties sheet for any file it is "sent to", ie context myfile.jpg will open the properties sheet for that app.