The simplest fix to lee would be to revert the last set of nerfs that deleted his atk speed slow on E and in turn make W jump work only on allied minions and champions. Boom, balanced.
Edit: let me try to explain. He was considered underpowered at the start even after the initial major buffs because he didn't bring team utility and wasn't particularly tanky compared to meta junglers of the time. Then meta changed a lot of things got changed and people figured out you could ward jump, he was strong in skilled hands then but still not overbearing. Then they released sightstone, a cheap health item that gave him 4 jumps that refresh every time he backs. That's when it got over the top.
My proposition would be to shuffle some of his utility from ward jumps back into dueling power with the atk speed slow on E. That would make him have to expend an important 5min CD summoner spell in order to perform what is now relatively easy and cheap to perform combo of Q Q ward W R back into your team (would then have to be Q Q flash R). Then he would have to think hard who to kick as he can at present kick a low priority target to win a skirmish and still have the ability to do it again easily for the next fight.
Edit 2: Oh and give him his shield back on W if he jumps a minion. If what I've suggested would be implemented he could return to top lane if he chose so.