Workflow in Mass Write-Off

I am looking for a solution for write-off, but have confusion about the function module at 5512 event. I want to trigger workflow for W/O amount > $1000, So should the FM be modified(sample FM is blank) to check the amount and if it is greater than export the check reason?

If it will do only this, then how the workflow will be triggered? or we need to trigger it in the same FM at 5512.

I want to trigger workflow in both mass and manual write-off.