Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - General Beta, Steam and DLC purchase question

I'm already getting the game through Steam once it goes final, that's not an issue, but I'd like to pick up the DLC while it's on sale. My question is, if I purchase it normally, will it attach itself to my timed beta, or will it eventually tie in to my final key? Should I buy it as a gift, and then apply it later (assuming I can do that, I never tried gifting myself before)?

I just don't want to buy the DLC, only to have it expire with the beta, and then have to deal with Steam support to get it fixed later.