I copied cmd.exe to C:\Program Files (x86)\BigFix Enterprise\BES Server\BESReportsData\CustomExe on the Web Reports server and create Scheduled Activities for the reports I want to export and use the Customized Executable: selecting cmd.exe and then enter
/C copy /Y <reportfile> "path\filename.csv"
<reportfile> represents the generated report, substitute a fully qualified path and filename as the target for the copy. Thanks to Jason for providing the code tags for above.