Board Thread:Dark Souls/@comment-184.20.120.245-20131108192146/@comment-6003396-20131210010634

Yes pretty much. Summoning him should be fine, since it is his dialogue that appears to be what triggers his storyline.

Basically:
 * 1) Don't talk to him in Anor Londo when he is by the bonfire.
 * 2) Kill the red-eyed chaos bug.
 * 3) Talk to him in Anor Londo, Sunlight Altar, bonfire after Centipede Demon, then Chaos Bug area – in that order (but you first need to enter Lost Izalith in order to get him to spawn in the bug area).

After all that he should be summonable for Gwyn.

I haven't yet done this myself, just summing up what the first AWC posted.