It's an interesting idea. I had planned something like this orignally but gave it up because of the cost in hammers (90 for the Monastery and 3x60 for the missionaries). Another issue is if we can produce the Missionaries fast enough. They must be available and have moved to the target city before we bulb Philo. Do we have enough foretst to chop? And do we have enough workers to do all this chopping. There must be free workers turns to improve our resources. Right now my main concern with this approach would be the worker turns used for chopping. I was desperately short of workers during the test game I played. And we are, of course, using 150 extra hammers.
There is a good chance that either Athens, Timbuktu, Carthage, or Ivoryville will become the Holy City, in which case Ivoryville would only need to produce 2 missionaries. And as long as we have Carthage converted by the time we change to Pacifism, the GSs wont be delayed. If Athens gets its missionary a couple turns late, it wont affect its GS because it has to keep its GP points in check anyway while Carthage and Timbuktu get GS number 2 and 3. Using Organized Religion instead can present a different problem: not having enough missionaries built by the time Philosophy is bulbed. A monastary can build a missionary any time.
If we go for the Organized Religion approach, we still need to produce 1-2 more missionaries quickly, and this will still probably involve chopping somewhere, though not as much chopping as with the monastary approach. We definitely need more workers.
The monastary approach wont work very well if Ironsite or York become the Holy City because they dont have enough forests to build a monastary quickly.
With a little luck Carthage will become the Conf holy city and that will make things easier. It happened in my test game and I read somewhere that the largest city (not counting the capital) without a religion is most likely to become the holy city.
Here is how the Holy City is decided:
Once it is decided that a certain player founds the religion the game assigns a value to every city of the player as follows:
the city gets an initial value of 10
the city gets +1 for each population point
the city gets a random +0 to +10
This value is divided by number of religions the city already has +1
IF this city is the capital the value is divided by 8
The city with the highest value wins. Ties as always are broken by the oldest city winning (since the game only lists one "Best Value" and only changes it afterwards if another value is higher).
So it's mostly random with higher population cities being favored and the capital being effectively disqualified. Hopefully we get a bit of good luck this time and one of our GS cities becomes the holy one.
Curious why the missionaries must in their target cities before we can bulb Philosophy?

Should I know this answer??
They don't. They do have to be there for Pacifism to work in that city. But if we order the conversions 1) Carthage, 2) Timbuktu, 3) Athens, it wont matter if Athens doesn't have its missionary when we switch to Pacifism. Carthage is the bottleneck.
Philo will also give us Taoism, a second religion.
I think Pacifism only works for cities with our national religion, which will be Confucianism.
In all my test games, Ivoryville became the Confucian Holy City. I think it was because Carthage was in resistance at the time?

Could that be?
I've never seen a city in resistance become a Holy City. I'm pretty sure its impossible. If Fred got Carthage as a Holy City in a test game, it must have been that he captured it quick enough for it to come out of resistance before CoL was done. This is another good reason to capture Carthage quickly. If we can draw out a settler party from Carhage soon, we might be able to take it before all of our units get there.