I had given this a shot today with my soda carbonator. I went for two litres; normally for regular salt water I use four.
I had carbonated warm water, and the solution flowed into me quite well, not really any slower or crampier than normal water. I actually enjoyed it, because despite the water being carbonated, it didn't hurt at all, and when I shook my belly I could hear and feel it a bit. I would reccomend to anyone curious to try, however, I do not know if it actually is safe or not. Always exercise caution.