I soaked the beans in about an ounce or so of the bourbon for a few weeks (was only supposed to be a week, but my brew schedule kept getting pushed out and the beans were already soaking) to sanitize them before adding to secondary. The bulk of the bourbon (I used 8 oz.) was added when I transferred from secondary to the keg.
Edit: No, this isn't what I did. I'm remembering incorrectly. Jeez, it sucks getting old.
It was the oak chips that ended up with an extended soaking in the full 8 oz. of bourbon for about 3 weeks before adding to secondary. I can't remember what I did with the vanilla beans. Might've just added them to the end of the boil. I'll check my notes tonight and update this post... again.
Edit 2: Evidently, I soaked the vanilla beans and the oak chips in 8 oz. of bourbon and dumped the whole mess into the secondary for about a week, then I kegged and let it age for 4 months before tapping. Fortunately, I don't need to refer back to my notes to recall that it turned out to be really nice brew.