I've found a solution in case anyone comes across this post and would like to do the same thing ...

First, install AutoHotKey ( i don't remember the url).

Create a new AutoHotKey script. It will run like a program as long as it has a .ahk extension.

I added the file 'rightclick.ahk' to c:\apps folder (you can choose wherever you want).

The code I added inside the rightclick.ahk file (below the commented out text automatically added in) is the following, single line --

Send {AppsKey}

Save it.

Now to map the calc key to the AHK script --

Go into the registry

hkey_local_machine -> software -> microsoft -> windows -> currentversion -> explorer -> appkey ->

mine is item 18 (calc key on m2800).

I modified the shellexecute value to 'c:\apps\rightclick.ahk' (no apostrophes).

Closes up registry, hit 'Calc' key and contextual menu appeared.

I hope this helps someone.