I have a Jurek and a PB vest and I run soft flasks. I run the excess bungie material over/around the lid to keep them from flopping out then run straws so I can sip with them in place.
YMMV, but that works for me. You're a smart guy, you'll think of something.
http://www.paksitphotos.us/2016-C100K/1/i-JmTqSzN/...