You could build a C/C++ DLL with a data segment amongst all processes that load the image and have it act as some kind of broker (thinking out loud :-)). I am however in total agreement with Ed's reply(s), a lot easier with a lot less to go wrong.

Example:

// Make a new shared section.
#pragma data_seg(".shared")
char szSomeData[] = "ABCD";
#pragma data_seg()


Don't forget to tell the linker about it in the flags with the Read, Write and Shared switches:-

/SECTION:.shared,RWS