If you can verify that your iMac has the necessary mounting points, you can use this kit (see link below) to install the SSD drive while retaining your Super (DVD) Drive.
http://www.yourmacstore.com/internal-ssd...
If the above won't work for you and you don't want to mickey mouse mount the SSD, you can use OWC's data doubler kit to replace the Super (DVD) Drive (link below).
http://eshop.macsales.com/item/Other%20W...
If you go the above route, you'll also want to make sure the SSD is connected to the SATA III port on the main board of the iMac since only 2 of the 3 SATA ports on the Mid 2011 iMac are SATA III compliant.
Although, this is only relevant if your SSD is SATA III.