I've just had (or still having?) a period of DS waking earlier but still being tired. Similar age too. I'm able to put him to bed earlier but even with the EBT he was still waking too early and being tired. We seem to be sort of out of it now, I think the EBTs really helped but I see you can't manage this most days - can you do weekends perhaps?
Have you spoken to him about going back to sleep in the morning? I know you have the gro clock and obviously he understands the rules on that, but an honest chat about needing sleep for energy so he can play well helped here, plus any time he yawned or looked tired in the day we mentioned it in a very supportive way.
I wouldn't give the opportunity to turn a light on and read books pre-7am if that's 'morning' because it goes against what a gro clock is and does, you want him falling back to sleep for that last hour not reading. However, DS has lights on a timer rather than a gro clock for this very reason, he's always read when he wakes. If you want the option of a lamp you could plug one into a digital timer so that power goes to it at 'morning' (7am) but the lamp doesn't work pre-7am as that is still 'night'. We just have the lights come on at WU time, it does occasionally wake him if he's shattered and are now doing lie ins at the weekend.
