well you can cut a branch off of a plant stick it in a cup of water and leave it there for a long period of time and it wont wilt. it wont so anything actually but it will stay nice and green.
to the OP, i understand what your saying, its not convienet for you to get all that water to your plants to flush as they probs outdoors in a secret spot or w/e. i guess if your that hellbent on flushing and not satisfied with just watering with straight water 2 weeks befor harvest you can cut em and try and get them to take a root, then flush them? this seems like alot of extra work for the minimal difference in taste, personally just feed without nutes for a couple weeks prior to chop and call it a day. up to you tho