Not while you are doing the MC, but just generally when you are preparing for doing the liver flushes you might try taking 1/2-1 tsp of Epsom Salt in water on empty stomach in the morning for 2-3 weeks.
This will not only help keep your bowels moving, but will also dilate the bile ducts and start clearing them out to some degree as well -- which is really important when it comes to the flushing.
I'm also a big fan of a series of colonics using a closed system, if you can afford it.