Online RAID1 -> RAID10 migration?

Hello,

I'd like to know if it's possible to do online RAID1 -> RAID10 migration with md. I ran a little experiment and it seems my approach doesn't work:

jo test # mdadm --detail /dev/md7
/dev/md7:

        Version : 1.0

Creation Time : Fri Nov 25 23:29:37 2011
Raid Level : raid1
Array Size : 51188 (50.00 MiB 52.42 MB)
Used Dev Size : 51188 (50.00 MiB 52.42 MB)
Raid Devices : 2
Total Devices : 4
Persistence : Superblock is persistent

Update Time : Fri Nov 25 23:33:55 2011
State : clean
Active Devices : 2
Working Devices : 4
Failed Devices : 0
Spare Devices : 2

Name : jo.bartk.us:TEST (local to host jo.bartk.us) UUID : 5c6e806a:d91b8007:dce490aa:1442d468
Events : 19

Number Major Minor RaidDevice State
0 7 0 0 active sync /dev/loop0
1 7 1 1 active sync /dev/loop1

2 7 2 - spare /dev/loop2
3 7 3 - spare /dev/loop3
jo test # mdadm -G /dev/md7 -n 4 -l 10
mdadm: /dev/md7: could not set level to raid10 jo test # dmesg | tail -1
md: md7: raid10 would not accept array

Any advice on how to pull this off? Is it even possible? Can it be implemented? My root device is on RAID1 and I'd like to move it to RAID10 to get some write/read speed benefit.

Thanks,

--Bart