I breifly chatted w/Intel support, and they told me that, yes, this should be no problem. Have not yet tried it again, but will tomorrow.
My BIOS does does list any of the Intel-controlled SATA ports (0-5) on the page where the others are listed. I believe that this is somehow because the only two drives plugged into these are in RAID mode.
My experience,on ASUS P5Q PRO (P45+ICH10R)
Create raid with SATA port0,1,single drive on other port set as JOB mode.
of course you cant see it in M/B bios,do it in RAID bios
I'm curious to know whether you were able to add the single drive and have it recognized by the motherboard BIOS. If so, did you have to clear the real time clock to have the BIOS recognize the new drive? And if you *did* have to clear the clock, was your Raid0 still intact afterward?