I was at Jackie O's in Athens, OH for the most recent bottle release. Brad there had brewed a Chai stout with his Dark by 7 stout as the base. My wife and I both thought it was an incredibly delicious beer - esp with a steak and eggs breakfast. That said, half of the people loved it and half thought it was too much.
He used infusions in the secondary with a variety of different spices to great success. Unfortunately I never got to ask him what spices, the proportions, or the time that he used them. That said, you should be able to add the spices to the secondary and sample after 5 days, 10 days, etc. to see if it gets to where you like it.
Having messed with spice additions in secondary myself, the flavors come through a bit different once it's bottled and carbed. In the future I plan to brew a small test batch, pull off a few bottles worth at several time points and then bottle those with the individual carbonation sugar pellets to get an idea of what the different proportions do to the final beer. You'd obviously have to choose the time points ahead of time since you'll have to wait 1-2 weeks for these bottles to carb to try them.
I agree with the others that the addition of the actual tea probably won't work. When doing cold brewed tea you don't want to leave the tea in the water more than overnight; I'd be concerned that you might start getting a lot of tannin extraction if you're going several days or a week (which may be necessary to get a good spice flavor). Additionally, you certainly don't want to use store bought tea bags since they'll contain tiny leaves crushed to a small powder which will extract much quicker and will be tough to get out of the secondary - you should probably use either nicer tea bags or make your own; at that point, I don't see the advantage of using tea bags over individually bagging the different spices and tea. Anyway, good luck.
