OWC has released a Do-It-Yourself (DIY) upgrade kit for 2011 27-inch iMac owners. This upgrade kit will let them add a Solid State Drive/Disk (SSD) to their current hard drive.
The US $45 kit includes all the tools and the power cable needed to add the SSD (sold separately).
The process would requires you to remove the 27-inch glass display with suction cups. There is an installation video, which you can watch before you make your purchase. If the DIY kit is too complicated, you can still use OWC’s turnkey service which will install the SSDs for you.