Allow for secure delete of temp files?

This may already be there, but I don't see it. I'd like to be able to specify a secure deletion command to be used when removing temp directory contents. Something like SDelete, or Freeraser that will overwrite the file area on the disk.

WinSCP does not support this.
But you can configure WinSCP not to delete the temporary folders - a side effect of Keep temporary copies of remote files in deterministic paths:
https://winscp.net/eng/docs/ui_pref_storage
And schedule a task to delete the folders using any method you want.