[CentOS] Rescan for new geometry without reboot?

Hello,

We just had our servers fitted with more disks. Most of the disks are
growing existing RAID 1+0 channels, some are in new channels.
Controllers and disks support live installation.

I'd like to avoid a reboot just to let the system find that the disks
are larger.

All I can find so far suggests that its possible to rescan the disks,
and even find the new geometry (e.g.
http://linux.derkeiler.com/Mailing-Lists/Kernel/2004-12/1555.html) but
nobody knows how to actually convince the system to let me use the
extra space without a reboot.

Does anyone know of a way to achieve this?

Thanks,

--Amos