Hazelnut extract added to stout recipe?

I'm new to homebrewing, and still a little gun-shy on trying "out of the box" ideas before i really know what I'm doing. Right now I have some stout fermenting, and I've been reading about hazelnut flavored stouts, and I'm wondering if it's too late to convert this stout into a hazelnut stout? Would I just add some hazelnut extract right before bottling? Is this a bad idea, something I should wait on until I plan it from the start? It's just a basic stout recipe I bought from morebeer.com. Also, if adding the hazelnut at bottling is a good idea, where would I find the hazelnut extract? Thanks for any help!

I've made 3. Its SWMBO's favorite beer of all time.

Add the extract at bottling.

Being your first time, rack to your bottling bucket. Then add a little extract and stir gently (enough to mix it but not enough to oxygenate your beer). You'll probably want to have someone in another room to taste it for you. The first time I did it, the smell of the extract was so powerful that I couldn't tell the difference between what I was smelling and what I was tasting.

I have added 1 tsp, 2 tsp, and 2 Tbsp to my three versions of it. The last one is a bit much for me, but SWMBO thinks its perfect.

Bottle half of the batch and then add the hazelnut to the rest. Or maybe bottle 1/3, add a bit, bottle half of that and add some more. That way you can do side-by-side comparisons.

Oh, I forgot your last question. I got my hazelnut extract at the LHBS. I'm sure you could pick it up at a baking supply store. Maybe even the grocery story.

Thanks a lot guys, I'm going to try the half and half idea so I can compare.