I'd set aside a gallon and add just a little unflavored loose pipe tobacco. Sample every few days for a few weeks, then add more once it stabilizes.
I have thought about trying this myself. I think a tiny bit of pipe tobacco would be the way to go as well and brewing a 1 gallon test batch. That way if it tastes like complete ass you can just dump it (i have had to do this several times with my more experimental beers). I could see tobacco being good in the background flavors of the beer, but not a leading character. Maybe start with 1/2 or even 1/4 of a gram in one gallon, swish and let it sit for a week or so, strain the tobacco out, then give it a taste. If you think it could use more, add another 1/2 gram or so and repeat. I would think that with this method you would have less risk of adding far too much and having the beer be gross, or worse, be toxic.
Personally, i think if 12oz of this beer makes you woozy then there is way too much tobacco in it. Again, i could see a mild tobacco flavor being welcome in a darker beer (like the porter mentioned). If you give this a try let us know how it turned out.