Yes it's okay to take it with your juice, you don't have to but it's easier, for me anyway. I learned from Uny to take my dose of IF2 with the last little bit of juice that's in the pint jar. I like that because it's one less container I've got to wash! :)
If you have any charcoal you could take it in a little juice to adsorb/absorb the toxins being released, just be sure to drink enough water. Oh, and one thing I learned while juice fasting is to make sure you take the IF1 with a dose of IF2, don't know if you're using the #1 but it's always good to know.