There is a freeware utility called usbdlm (USB Drive Letter Management) which may help for your situation. It requires you to input specific info about each cradle it allows you to set the drive letter based on multiple criteria such as volume label or size etc. If each drive was given a unique letter based on its label or serial number then LR should see them as all different?
The 300Kb application can be found at
http://itknowledgeexchange.techtarget.com/...e-dissapointed/A friend was having trouble with the his pc assigning the usb drives the wrong letter then syncs would get messed up, and found this utility. It sounds like it should solve your problem
From the website:
USBDLM can for newly attached USB drives
check if the letter is used by a network share of the currently logged on user and assign the next letter that is really available
reserve letters, so they are not used for local drives
assign a letter from a list of new default letters, also dependent on many different criteria as the active user, drive type, connection (USB, FireWire), USB port, volume label, size and others
assign letters for a specific USB drive by putting an INI file on the drive
remove the drive letters of card readers until a card is inserted
show a balloon tip with the assigned drive letter(s)
define autorun events depending on many different criteria
many other things, see help file, available online as HTML version too
jpegman