SQL Server Backups in Parallel
Create additional jobs to run backups in parallel.  Make sure to specify a single unique database per job.  Configure the SQL Server Agent jobs to start the backup at approximately same time, with a 1 minute delay between each job.

You may find that running backup jobs simultaneously does not significantly decrease backup time.  You should evaluate the I/O capability of the disks where the databases reside, the disks where the backups are being written to, and in the case of network backups, the capacity of the network to transfer data.