WHM API 1 Backup Destination for start_background_pkgacct

Writing a web script that pushes backups to an ftp server of my choice using php and the json api of WHM 1. I have found start_background_pkgacct which pushes these backups to a folder as well as backup_destination_add which defines the ftp location. There doesn't seem to a way, in documentation at least, to tie the backup destination to start_background_pkgacct. I cannot use a cron job as this is a dynamic script that sets its own ftp address. I also cannot leave the cpmove file in the account. Looking for ideas here. The only reference I have found is based on CPanel API 1 which is deprecated and seems a bit incompatible with the jsonAPI of WHM 1.