As a workaround you could set entries in the fstab file to have then mount automatically.
By default the fstab file is not use in OS X however I use it as I have many external drives that have multiple partitions of different filesystem and I do not want certain partitions being mounted so I use fstab to stop OS X from automatically mounting in specific cases when plugging these drive in. So you could set your extra disks to mount automatically in fstab.
In a Terminal: sudo nano /etc/fstab
Add a line for each as in the example below however use the UUID (Universal Unique Identifier) for each volume you want mounted on each drive. You can get the UUID from Info in Disk Utility after selecting the target volume.
UUID=2F1EAF27-C132-32B6-8919-51D08398D4A1 none hfs rw,auto
For additional info on fastb, in a Terminal type: man fstab