I don't know if anyone followed this thread, but I have worked out a way to resolve all the issues I was looking for improvement on. I would have worked it out earlier, but work, life.... Now I have a cold so I had time to geek:
I worked out a means of moving the entire home partition to the sd card, still have a partition available on it to share via usb, and have them all mount at boot and yet not prevent my ability to remove the card and use the sd slot for simply storage.
The primary problem was that the sd devices were not initialized until late in the boot sequence, after the partitions listed in fstab were already mounted.
Mounting and unmounting of the sd devices is controled by the commands in /etc/sdcontrol. By rewriting sdcontrol I now have my first sd partition mounted on /mnt/card and my second on /home. If there is no second partition, it does not try to mount it. Since I found the original a bit, um, rough, I completely rewrote it. Feel free to use it yourself, but at your own risk.
A couple notes:
1) Copy the contents of your /home partition/directory to the second partition of the sd card BEFORE using this script or you will be lost without any files. For lack of rsync, I would use gnu-tar, being careful to preserve permissions with the -p flag. I am not going to outline how to partition your sd card or create file systems. There are enough threads about that.
2) I would leave a basic home partition on the internal flash, even if you never expect to use it. This is a good means of c.y.a. just in case your sd fails and you still want to log in.
3) Once you have inserted (or rebooted) with the sd card with the second partition that contains your home dir, you will not be able to unmount it unless you reboot. The reasons should be obvious: this is your home dir. It will be hard to create a situation where the files there are not active in one form or another. It refuses to unmount with good reason.
4) You can insert the sd card with the home partition while logged in and it will mount over the existing home partition/directory. It may break a few things, hopefully all resolvable by cd-ing to / and back, but so do it at your own risk. See above for why.
5) Once you are logged in on your sd card and you want to remove it, simply reboot, remove the card during the reboot process, and insert a different sd card with only one partition. If you did 2, then you are fine, with the sd card now mounted only under /mnt/card/
Blah blah blah, here is the new /etc/sdcontrol script. Its pretty simple, once you read it, so have fun hacking it to your own purposes. Always back up, of course! Please note there are plenty of easy to understand variables that you can change.