Not sure of a way to do it exactly. Hotplug may work but not sure.
Here is a thought but will require some scripting similiar to the one above. One could fake it to always mount to the same directory no matter the order it is inserted. No matter which device is plugged in first it will be /dev/sda. Now using hotplug to pull the ID of the device you can use that to mount that device to a specific mount point. I think that is what that script maybe acomplishing.
Hard to explain.
device 1 to mount to /mnt/usb1
device 2 to mount to /mnt/usb2
Now if you insert device 2 first it would mount to /mnt/usb1
If hotplug sees the device and identifies and knows to always mount it to proper directory then when
device 2 is inserted first then it mounts to /mnt/usb2
Not sure if this is actally what you are after.