Personally I don't like to take fiber during the fast. I feel it interferes with the body getting the fasting message, and doesn't let the bowels rest. But I have absolutely nothing to back this up.
However, I do blend the lemons instead of juicing
them, this gives my body some fiber to work with and uses more of the whole lemon.
There is a thread on here with the same questions and answers as you posted.
Some people like taking the psyllum. It's a personal preference that only you can answer.