Something which I have resisted saying for 8.5 pages, but will now say, is that you should really have tackled this issue a lot earlier. But, like me saying that, you've put it off an awfully long time. I hope you've managed to strike a diplomatic tone. The next stage is to work your way through the songs properly, and stop them whenever it goes titsup to tell him what's gone wrong. For one thing, if you're doing covers and he's getting the length of the solo wrong, he's not playing the original solo - that might be worth pointing out.