I had trouble mounting multiple swap FILES residing on different partitions but solved like this on the command line:
CREATE SWAP AS A FILE ON FIRST DISK DRIVE:
dd if=/dev/zero of=/mnt/sda1/swapfile bs=1M count=256
chmod 600 /mnt/sda1/swapfile
mkswap /mnt/sda1/swapfile
CREATE ANOTHER ON SECOND DISK DRIVE:
dd if=/dev/zero of=/mnt/sdb1/swapfile bs=1M count=256
chmod 600 /mnt/sdb1/swapfile
mkswap /mnt/sdb1/swapfile
FOOLISH THINGS:
uci set fstab.@global[0].anon_swap='1'
uci set fstab.@global[0].auto_swap='1'
CLEAN HOUSE:
while uci -q delete fstab.@swap[-1]; do :; done
AUTOSTART ENTRY 1 WITH A FAKE LABEL:
uci add fstab swap
uci set fstab.@swap[-1].enabled='1'
uci set fstab.@swap[-1].device='/mnt/sda1/swapfile'
uci set fstab.@swap[-1].label='foo'
AUTOSTART ENTRY 2 WITH A FAKE LABEL:
uci add fstab swap
uci set fstab.@swap[-1].enabled='1'
uci set fstab.@swap[-1].device='/mnt/sdb1/swapfile'
uci set fstab.@swap[-1].label='bar'
COMMIT AND REBOOT FOR PROOF:
uci commit fstab
reboot
AND WE HAVE SUCCESS:
free
Swap: 524280
w00h00!
Now you can plug and unplug hard drives as either sda1 or sdb1 while the power is off, and as long as one of them contains a swapfile file then it'll mount at bootup.