Can file-backed memory disks act like slices?

[Michael Dexter]

Hello all,

I trust this is a Seldom Asked Question...

I am using file-backed memory disks (as in mdconfig -f) to prototype 
filesystems.

root.img gets mounted first and usr.img, var.img and tmp.img get 
mounted below it and as such they are behaving as partitions.

Is there any way to get a single memory disk to behave like a slice 
and itself be partitioned? That would give essentially:

/dev/md0a
or even
/dev/md0s1a

This would allow the four partition images to be combined into a 
single partitioned image.

Yes, I have a legitimate use for this. :)

Appreciated,

Michael.