[G4] Join Two HFS Volumes?

[Carlos]

I've got a G4 file server and I periodically have to add storage.  
With drives as cheap as they are, I've been picking up a bigger ATA  
drive every once in a while when they go on sale and adding it to the  
machine. The thing I haven't been able to figure out is this: How can  
I mount a drive so that it's file system is a branch off the startup  
drive?  In other words, rather than a separate volume in /Volumes/ 
whatever and appearing on the desktop, I want to mount the new drive  
under a specific node or path of the root (startup) drive.

And before you say "just use an alias" (or a sym link), this doesn't  
work when accessing the volume from a network host.

I know I can setup a RAID using the ATA-133 controller I have, but  
that means that every time I add a drive, I have to re-format the  
RAID, and I have no need of the performance boost of a RAID 0 anyway.  
What I'm really looking for is something like the old "join" command  
under DOS. (yeesh, I'm dating myself) which splices the file system  
of one drive onto another.

I've read about the "union" option of the mount command, but that  
appears to be under BSD formatted volumes only, and I'm not sure I  
understand the function anyway.  Has anyone done something similar,  
and if so, what is the best approach for my situation?

TIA,

Carlos