Try slicing your backhand down the line. When someone hits you a low slice, it's hard to hit the ball back down the line. The natural tendency is to hit it back crosscourt over the low part of the net. That might force your opponent to hit to your forehand, setting up the classic lefty play crosscourt against the righty's backhand.
Another thing you could try is hitting to your opponent's backhand side, but not going out too wide. I do this when I play lefties (I am a righty). If they hit a backhand, they have to hit it a little bit inside out to keep it away from your forehand. That's a harder shot, so they might just go to your forehand. If they step over and hit a forehand, they don't have any angle to run you off the court on your backhand side. And that's the real key for either player in that situation. You don't want to go out too wide to their forehand because that gives them the angle to get on your backhand. Better to play more down the middle or slightly to their backhand side to take away that angle. Usually the lefty has the spinny crosscourt forehand, so I'm trying to avoid that shot more than I'm trying to set up my own crosscourt forehand.