create multiple SquashFS partitions

Hello

I'm working on embedded platform (Broadcom's bcm5358u processor with MIPS
core), where I need extra partitions for the purpose of further upgrade
procedure. The filesystem used is SquashFS, so I modified 'struct
mtd_partition' accordingly, which is passed to MTD related code, and I ended
up with this (dmesg snippet):

Creating 7 MTD partitions on "sflash":
0x00000000-0x00020000 : "boot"
0x00020000-0x00600000 : "bank1os"
0x00188820-0x00600000 : "bank1fs"
0x00600000-0x00be0000 : "bank2os"
0x00788820-0x00be0000 : "bank2fs"
0x00be0000-0x00ff0000 : "app"
0x00ff0000-0x01000000 : "nvram"

#cat /proc/partitions
major minor  #blocks  name

  31     0        128 mtdblock0
  31     1       6016 mtdblock1
  31     2       4573 mtdblock2
  31     3       6016 mtdblock3
  31     4       4445 mtdblock4
  31     5       4160 mtdblock5
  31     6         64 mtdblock6

#cat /proc/mtd
dev:    size   erasesize  name
mtd0: 00020000 00010000 "boot"
mtd1: 005e0000 00010000 "bank1os"
mtd2: 004777e0 00010000 "bank1fs"
mtd3: 005e0000 00010000 "bank2os"
mtd4: 004577e0 00010000 "bank2fs"
mtd5: 00410000 00010000 "app"
mtd6: 00010000 00010000 "nvram"

Now I want to be able to mount /dev/mtdblock4 as a temporary storage during
system upgrade, but I can't do this, because it appears that this partition
mtdblock4 doesn't have any FS installed. The kernel image and FS are
integrated in one image, which is flashed down the /dev/mtdblock2 (which is
supplied as root_fs to kernel).

I see only one solution: create a empty squashFS image, write it on
/dev/mtdblock4 and may be it will work as I want (?).  Is there a way to,
like, format the partition on the fly, whenever the kernel boots, or it
violates the MTD concepts?

Thanks.