Our nearly 5 ds has similar bouts of stubborness but usually crashes when left in semi darkness to unwind. However we have also found that story tapes(one side and then sleep) and a side lamp help (probably a dimmer would be better).
Has he recently started school or extended hours as it may be the buzz of the school day is keeping him alert later while he is not as physically tired.
The reward system sounds a good one if you can stick to it, as does maintaining the early evening routine. Perhaps get firmer with him over the weekend or half term when you are under less pressure to get him out to school in the morning. Nothing worse than dealing with an over tired child when you need to get out of the house by a fixed time, especially if you are tired yourself!!
hth
LizS