This is very possible as I just did it today on my advy.
Requirements: 1. Neutral alignment.
2. Positive faction with both redeemed and unredeemed.
3. Several copies of the Weary Empath pattern ready to cast.
4. Six insignias for Roch. (not the 6 for ocra.. didn't need those)
I had completed both Scheol garden keys some time ago, so I thought I would revisit them and get the sanctuary keys for good measure.
1. I went to each garden and talked with the quest npc to get the sanctuary ball rolling. I received my unique Cloth back and was told to show this to the Weary Empath after summoning.
2. Okay.. at this point I started to the incarnator and summoned the Weary Empath. I showed her the cloth, did the talking and she talked about Miller.
3. Went back to the Sipius in Ocra, told him about this. I was told to take care of the Eric Miller problem for good!
4. I then went to the Unredeemed Temple and with the aid of a friend, took out the Prophet. A little guy appeared telling me to feed him six insignia to get Eric Miller out to play. This is where you use the six insignias.
5. After killing Eric Miller, loot the defiled pattern of Ming Liu and head back to the Ecclesiast in the Redeemed Temple.
6. After seeing this..he will send you up to ergo to tag the ancient machinery there. Run!
7. Once back at the Ecclesiast, he will summon Ocra to bless the defiled pattern for you.
8. Run back to the incarnator, cast the Weary Empath (Your SECOND complete pocketboss) and show her the now blessed pattern. She will give you the Essence of Patience.
9. Run back to the Ecclesiast, hand over the blessed pattern and get your new Sanctuary Key!
Now from here I debated on what to do about the Roch sanc key. I noticed that from all the dealings for the Ocra quest, my Roch quest had now skipped up a few beats. Very strange.... (major neut loving).
10. I went to see Eric Miller in Roch and told him about the unusuable blessed pattern that we suddenly had (which you don't now cuz you turned in for your ocra key).
11. Here I noticed that instead of Eric Miller asking for the pattern.. I now had the blessed pattern in my inventory.
12. I saw that my mission then was to talk to the quest npc in the Unredeemed Temple.
13. Once there, he wanted me to go tag the machinery up by Ergo.. (run, run.. tired!)
14. Once back and breathless, he summoned the all mighty Roch (I expected a better view of this guy) to defile the pattern for us.
15. I was then commanded to use the defiled pattern and kill the Weary Empath.
16. Rush to the incarnator, summon (your THIRD complete pocketboss) the Weary Empath, dispatch this poor soul and your mission completes.
17. You already have the defiled pattern, cloth (now not needed), and the Essence of Patience (from the ocra quest as it's not taken).
18. Rush to Roch, talk to Eric Miller, hand over the defiled pattern and receive your new Roch Sanctuary Key!
19. You are left with the Cloth and Essence of Patience for your souvenir collection.
So after 3 completed novictalized patterns, six Roch insignias and a few hours, you can have both sanctuary keys for your very own.
Thanks for the guide. ;)