Dragon Age: Origins
Now to my question; in my second play through, would it be possible to side with the Templars, but still use the Circle (or whats left of it) to free Connor without killing anyone?
I don't think so, but feel free to try. Even if the First Enchanter seems friendly with the Templars it's more about being courteous. You could use the Circle to save Connor without any sacrifices, but siding with the Templars might be seen as a hostile action from the mages and they may be reluctant to help you.
Read some of this or all of it, whatever floats your boat.