"Fusion drive" is just a gimmick. Very transparent to the user, but it's pretty much an mSATA SSD and HDD combo. That will go away once SSD's are more affordable.
Your iMac has a 2.5" HDD slot, so if you just have an SSD in there, you can upgrade it yourself and make it into a "fusion drive". There are plenty of tools out there and people have made it work on systems that didn't come with it by default.
Your iMac has a 2.5" HDD slot, so if you just have an SSD in there, you can upgrade it yourself and make it into a "fusion drive". There are plenty of tools out there and people have made it work on systems that didn't come with it by default.