I am still looking for a solution to this after 25 years of trying! I too teach middle stages composite (p3/4/5), and think your rolling programme idea is definitely worth a try - even better if you have support from a classroom assistant in order to keep the rest of the children on task. When I have worked like this, groups have responded well and been much more focused on the lesson. One of the pitfalls I found was that I felt it took a long time to cover all the work with all the groups, but reckoned it was worth it for the quality interaction and writing produced. At the moment I too am teaching whole class lessons because I don't have a classroom assistant to supervise independent groups.