I have successfully rooted clones cut from plants 3-4 weeks into flowering and had good results. People think its impossible to cut clones after a certain point in flower, but to my knowledge you can clone at any time with some success. There is no reason you can't - it may be tougher but the fact is, the stem still contains the hormones needed to make roots. Try cutting a fully formed bud (a smaller or less-dense one of course!) the week before harvest. I bet it will root just as fast as a normal clone cut from a flowering mother. Then when you start flowering that clone, a new branch will start to grow from every calyx on the bud (in theory).
Then again, I could be wrong
There might in fact be a point during flowering when cloning is no longer possible.