ODBC connections are something I understand more in theory than in practice, but If the data is in FileMaker and the calculation is in MySQL, then I don't think the MySQL back end has any way to access data in the FileMaker file. I believe FileMaker can "see" the MySQL tables, but doubt that MySQL can "see" the FileMaker tables.
the calculation is not done on the mysql end i think.
i have added a remote table to filemaker and in filemaker edited the field options to calculations. so that filemaker is doing the calculation and updating the remote field. i would assume that if that was not posible the option would not be there