No, the iDRAC cannot do this, but you also do not need to have it down for 10 hours. You only need it down long enough to START the expansion - it will finish while the system is live and operational (although in a slightly degraded state).
This cannot be done from the RAID BIOS either (depending on your controller and firmware level).
Which controller are you using?
I'm sure someone can comment on whether/how to run OMSA in your setup.