q77 raid capacity expansion?

I'm trying to expand a RAID5 volume with an additional disk on my Q77-based motherboard, but I get no Add Disk option in the Intel RST application.

Isn't this supposed to be supported? (I'm looking at Capacity Expansion support in http://www.intel.com/support/chipsets/imsm/sb/CS-022304.htm and assuming Q77 maps to the PCH column)

Thanks

Mike