You set control variables for MFFTP in an Enterprise Server for .NET JES region as follows:
You can use an optional ENVVAR DD statement to specify control variable values. You add this in the JCL STEP that runs MFFTP. This can be a physical dataset or instream data, as in the example given in Running MFFTP. The advantage of using this approach is that the values pertain only to the current execution and override any values set within Enterprise Server Administration.
//ENVVAR DD * MFFTP_KEEP=Y