What did you try exactly, and what happened/what did you see? You did not mention anything that leads me to believe you were attempting this in the right place
The PERC 5/i can definitely do it:
With the disk inserted, go to OMSA, Storage, PERC, Enclosure/Backplane, Physical Disks, and make sure your disk is showing Ready.
If Ready, go to OMSA, Storage, PERC, Virtual Disks, choose Reconfigure from the dropdown menu for your RAID 5, follow the wizard to add the disk.
If the disk is showing Foreign, go to OMSA, Storage, PERC, Information/Configuration (link at top of page), choose Foreign/Clear from the dropdown menu, then follow the instruction above.