Feature Request: --targetdir option on backup-begin

Hi, i just playing around with the "new" backup API for switching from the old way and simply want to do full backup's in push mode. If i do so, virsh backup-begin <domain> the backup-Image files are always created in the image directory As the place on the fast nvme's, where the images are lying is very limited, i want to place the backup-image files to be on another harddisk on an mounted dir whithout temporary save them in the image directory. To do so, an --targetdir option on backup-begin would be very useful. best regards Michael