As far as i'm aware it should be ok... fluid is fluid. The only time you need to be careful is if it's tea/coffee or fizz like Dr Pepper or Coke Zero, as these contain caffeine and caffeine is a diuretic so effectively it dehydrates you. You can still have them obviously, but just not alone x
I used to have a cup of bouillon a day when I was on Cambridge and it didn't seem to do any harm. There's a low salt version if I remember rightly which is probably better. I considered it to be like their savoury vegetable drink (only cheaper!).
I used to have a cup of that followed by a Cambridge mousse in the evening so it felt like 2 'courses'. Obviously, there isn't a mousse option on Exante but I suppose the same principle applies.
At the moment, as it's early days for me, I don't want to stray from the very narrow path but maybe later I may bend things a bit to make life a little easier.