This can be done but why do you need to call it on the validate event and what parameters are you trying to pass?
I agree that the AftValidate time is an unusual time to call it, but the basic logic would be as follow:
FDMEE calls a .bat file
the .bat file calls a MaxL script
the MaxL script does whatever you want the script to do.
In our example, we're using it as a BefImport script that calls a MaxL script to export data to a database that the remainder of the BefImport script then grabs for the Import process.
Not sure why you would need that on Validate, but the same concept could apply.