Setting a windows environment variable.

I am trying to set a windows variable in COBOL that I will be able to read in a C# program I am calling from COBOL.

"SET testvar=xx" works at a DOS prompt.

However the following does not work.

move "SET testvar=xx" to AFLD60
CALL "C$SYSTEM" USING AFLD60, 97 END-CALL. | Called ASYNCH so no delay

Any ideas would be most appreciated.