Add Failure Groups to existing diskgroup

Hello All,

On an 11.2.0.2 Cluster with 1.2.0.2 Dbs running  

In ASM I Have a diskgroup  with 6 Disks on two different hardwares. But Failure groups have not been created when the ASM has been installed.

Is there a way to create failures groups online when the ASm contains a lot of Data ?

The doc for alter diskgroup specifies that the failure group clause has to be used for new disks :

http://docs.oracle.com/cd/B12037_01/server.101/b10759/statements_1006.htm

I can remove a disk let ASM rebalance then add it again in a failure group. But It will be a long operation and I'm wondering if there is a shorter way.