Having read numerous books and threads on the topic it seems that the consensus when making a ganache is to temper it on a marble slab as a final stage before moulding/dipping. In an effort to speed up the process (and because the slab I use is just too small to be useful) I thought I'd just add 1% Mycryo cocoa butter to the ganache as you might do when tempering just chocolate. It firmed up nice enough but I don't know if it has the same effect as slabbing the ganache in terms of improving texture and shelf life. Has anyone else tried this? Does it do the same job?
Personally I find the easiest way to temper ganache is to let your cream cool down to approximately 30-35°C and pour it all at once onto the molten tempered chocolate. Then thoroughly mix it until you have a smooth emulsion. Since the temperature never gets high enough to take the cacao butter crystals out of temper you will end with tempered ganache.
I've had (and made) ganache both with tempered and untempered chocolate. Personally, I prefer untempered chocolate in my ganache plus since I temper by hand it saves me a good bit of time when making ganache. Have you considered not tempering your chocolate for your ganaches?