Learn to control the match like you're doing AND win at the end. Work on that.
Of course this makes them think they're just as good as you or better if they win, but that's when you sometimes bring out one of those 6-0 or 6-1 sets to wake them up.
This was something I used to do with girl from a mixed team I played on that kept blaming me for when we lost our matches. During practice I of course wanted to play a lot more than if I just came out and won 12 games and left. I wanted to stay out longer, so I'd extend the matches. A few of them kept saying how we were very close in capabilities because the sets were so close (7-5, 7-6, etc). Well, let's just say the next time we practiced they went home with donuts and breadsticks. I got asked why all of a sudden the score was so lopsided. I told them I like playing for longer than just an hour. They got the gist.
Now I also play with a few friends who I sometimes lose sets to 6-3 or less. I do it to work on my mental focus and to get used to how it feels to be down a set and work your way back into a match. Sometimes I do it when I'm working on improving something else like a certain shot or serve or something else in my game. It's always funny how they're always like "Yeah, I'm kicking your ***." Yep, you are... and I'm working on other things. Thanks for helping out.