If this is an employee of the financial institution, I'm sure FinCEN would be interested in this report, and it would clearly be in good faith so no one would criticize you for submitting it. You may not have a name, but you've got some money mule's account number.
If you really don't want to file, I would assume your documentation would include the fact that a single pay period is less than the filing threshold. Also, we've had customers fall victims to redirected payroll scams that weren't discovered for months, so while I think one pay period is a reasonable amount, there is not necessarily a ceiling for the at-risk amount in this case.
In my opinion, the only safe choice is to file, whether you consider it voluntary or not.