Yeah, only good way I know of is to be a mage using the crystal sorceries. Could get him if you had high, I mean HIGH, fire defense, when he lands in the center. Otherwise, you go up the tower behind it that has the black knight. (He has a greatsword over his shoulder.) One arrow to the back and the dragon flies off its perch, glitches, and dies moments later. If it doesn't show up, leave the Parish area -- make sure the area title loads, Darkroot Garden, Basin, etc. -- and return to reset him. Quitting and reloading may work, but unsure. The knight started chasing me on my second attempt to reload and test it.
Real pain in NG+, since I failed to do Solaire in the right way to get him to survive. And he might not show up for talk in the next location of his occurence if that dragon's around by then still... Know he didn't show for me.
Might be able to do it if you lure him onto the bridge while near the staircase, run out, hit once, then run under the steps. But with all the times he's killed me by flying straight up and burning me, I've gotten where I don't mind using a glitch to kill that ass... Especially when he manages to get back to the perch before I finish the job and it heals up.