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.

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.