You can definitely add them in post and make it look real, it just takes more work than what I did...accurate scaling & depth, artificial lighting, softer edges, blending layers, etc...Dropping the bottles in with a software program gets them in the shot, but does it look natural? How would you shoot the shot with them in there? Scott's idea would add 2 new lights and some hot spots on the glass.
You're adding two glass items into a shot that has nothing reflective or transparent in it. There is gonna have to be a little change to the lighting to accept the reflective stuff you've added.