Convert raidz2 to mirror ?

I have a pool created thus:

         NAME        STATE     READ WRITE CKSUM
         tank        ONLINE       0     0     0
           raidz2    ONLINE       0     0     0
             c1t2d0  ONLINE       0     0     0
             c1t3d0  ONLINE       0     0     0
             c1t4d0  ONLINE       0     0     0
         spares
           c1t5d0    AVAIL

on the basis that we had far more storage than we'd ever need, and it 
was good to go overboard on the redundancy.  2= years on and that's no 
longer the case of course.  Is there any way to convert this into a 
bigger pool, with at least single failure redundancy, without dumping 
the data, recreating the volume and restoring ?  I know I can't just 
expand a raidz2 by taking the spare and adding it as a live disk (yet 
?).  Is there any way, starting with the above, I can end up with, say,

     tank
       mirror
         c1t2d0
         c1t3d0
       mirror
         c1t4d0
         c1t5d0

without dumping, destroying, recreating, and restoring all the data ?  
Really I'd like to end up with

     tank
       raidz2
         c1t2d0
         c1t3d0
         c1t4d0
         c1t5d0

but I think that's a work-in-progress ?

Rob

-- 
E-Mail:	[email protected]		PHONE:  +44 24 7652 3037
Rob McMahon, IT Services, Warwick University, Coventry, CV4 7AL, England