What adapters are available for a connecting a secondary SSD to the Superdrive's SATA cable?
Should be similar to the one I got for my MacBookPro, actually here is one especially for iMacs:
OWC Data Doubler  

I got another one from ebay for ~20 $ - does not fit perfectly, but is good enough for me. Up to you which way you go.  

MacBookPro installation was not too difficult, don't know about difficulty for iMacs.