I know this prolly doesn't help, but I've got 5gal of this in primary right now.
Based on the comments, and the fact that I LOVE hazelnut, I bought an extra bottle of hazelnut extract. So I'll be adding both of 'em at bottling. There's another thread I posted in regarding extract, that has a few experiences of other brewers adding it @ bottling. I'll subscribe to this thread and try and update in a few weeks after I try the brew.
feel free to PM me in 3-4 wks and ask how it was, just in case I forget to post here again. I'll be excited to have an alert when I login to HBT
EDIT: found the nut extract thread: http://www.homebrewtalk.com/f39/adding-nut-extract-350586/