I know that Stonehedge uses prune juice and has had great results. I'm not sure if he takes it at night, in place of the ES...but I don't see why you couldn't do that, too.
One of his most successful Liver Flushes was the last one when he took Gold Coin Grass (www.sensiblehealth.com - some people like the GCG others just do the flushes - we all have different results and likes/dislikes etc...so I'm just re-telling what Stonehedge told me) for 6 weeks....then before he took the olive oil/grapefruit mixture he lay in a hot hot bath for an hour or so. Then he took the OO/GF and went to bed...in the morning (8 hours later) he took his first cup of prune juice...then 1/2 hour later another cup....I think he swallows 4 cups this way.
He said that that was his best flush as it took away his aching gallbladder and he got some great stones out!
So...it's totally possible to have good flushes without ES (Blueduck has 'em too)...it's worth a shot and it's not harmful...