To help everyone struggling with liquid diet!!
Besides extracts, you can add sugar-free syrups from Torani or Davinci; they come in loads of flavors - coconut, Kahlua, banana, peppermint, raspberry, and more. They both have their own sites, or you can order them on Amazon.
Best of luck to you. The pre-op and post-op liquid diet stages are the roughest part of the whole WLS process. You can get through these stages because it's evident you're willing to put the work in!
Mary
I don't know the "official" answer re sweeteners - I don't recall them being mentioned one way or another by the NUT or surgeon.....but I look at it this way: Four packets of Splenda (4 shakes) is less damaging than all the junk I ate pre-op. How healthy is fast food, fried food, ice cream, chips, or soda, etc.?