We've done this with and without computer-based curriculum (ALEKS). The year DS turned 7 he was just becoming ready to do his own maths in class without input from the teacher, which made everything much easier. We just gave him a textbook that had plenty of exercises and a clear style (I did pick that with care). Talked about what he'd done, and planned what he'd do next, at home/on the bus, and sent regular emails to his teacher so that she was in the loop, but she left it to us. The telescoping just happened naturally because we weren't taking notice of any schedule. We were trying to spend as much time as possible on problem-solving, too, which I recommend, but felt he needed to get some new material too; ended up being nominally two years' worth.
