how to convert to RAID-1 in place?

[Jack Howarth]

    I have a machine that has been successfully upgraded to
FC5 from FC4. However we would like to add a second drive and
convert the existing partitions on the disk to degraded RAID-1
paritions then add the missing slices from the second drive.
Has this procedure been documented anywhere? I know this is
possible under both Solaris and MacOS X, but haven't found it
described for Linux anywhere. Thanks in advance for any help
on this issue.
             Jack