I am something of a n00b so please forgive me if I do not use the correct terminology, or if this is a stupid question:

I have a usb thumb drive and a usb harddrive (HD in enclosure).
I have the folowing in fstab:
===========
none /mnt/usbstick supermount dev=/dev/sda,fs=vfat,--,umask=0,iocharset=iso8859-15,codepage=850 0 0
none /mnt/usbhd supermount dev=/dev/sdb5,fs=vfat,--,umask=0,iocharset=iso8859-15,codepage=850 0 0
===========

Both devices work perfectly if I plug in the thumbdrive (sda) first and the ext HD (sdb) second.
The thumbdrive can be unplugged and replugged and is still accessible through the MDK 10 supermount icon, however, if the HD is unplugged and replugged, its ID is changed from sdb to sdc (and then to sdd etc.). To get it back to sdb I have to reboot.
If I plug in the HD BEFORE the thumbdrive, the HD is assigned sda.
Is the any way that I can lock a given device to a specific ID, ie. the usb HD should always be recognised as sdb, regardless of the plugging order?

Well, I have decided to bump this, but simplify the question:

Is the any way that I can lock a given USB storage device (external HD, USB stick, whatever) to a specific ID, ie. a usb HD should always be recognised as sdb, regardless of whether it is the first or second USB storage device to be plugged in?