Any ideas for hiding pregnancy during family events.

I have a family gathering end of July and I don't know what I'm going to do about not drinking. My cousins and siblings have a big party and are big booze pushers so I need a good plan. I was thinking of maybe buying coolers and pouring out the alcohol and filling it up with some type of juice/drink lol . I don't know how I would get the lids back on though. I can't tell them I'm preggers so that's not an option. My sister in law is always on my tail making sure I'm drinking so it would be hard to "dump" or fake it. Any suggestions? :)