Nothing revolutionary but we used to do several of the basics with our HS team...
* heavy specific T work
* heavy specific front toss rounds
* front toss cage competition - "X out of six" or "X consecutive" hard hit oppo balls
* specific on-field bp rounds
* bp competition (tunnel of cones sent up in OF slightly oppo of center and slightly inside the foul line - "X of 6" hard hit through the tunnel)
* live scrimmage with one or two OF's, two oppo side IF's (plus a 1b if LH hitter). Coach pitch. Only oppo field is in play. Make pull side an automatic out while oppo foul is just foul. Coach pitch (or machine) from the mound keeps hitter properly squared - prevents the closed cheat.
Of course, all of this has to come with proper instruction along the way. Particularly on tee and front toss rounds, there would be consistent feedback on things like staying on and through the ball longer, letting it travel, the importance of not letting the barrel get below the ball, etc. I know the barrel below the ball is a contested POV but the tendancy with hitting oppo is for the barrel to drop and weak pop-ups the result. So, this teach worked for our HS teams. "Drive through the 3-4 hole" was a common visual teach.
Also, we didn't just teach oppo based on pitch location. We taught oppo as the first thought when recognizing breaking ball. Then, if it hangs, the body will automatically tell you to turn on it. This helped most hitters quite a bit with general handling of CB's.
That said, there are some players who are better off left with their pull approach. They just need to be on top of the plate more so that they can safely let outside pitches go. But, we would only arrive at this exception approach after extensive efforts to help them become a complete hitter.
PS - we found over the years that you need to provide the right mix and timing of oppo and straight up hitting drills and reps for a majority of young HS hitters. If there was a particular overload of oppo work over the course of a few days or even a full day, the hitters would struggle the next day with inside stuff. As example of proper mix, we may have three cage groups working. One would be oppo work, one would be something else and then we would finish with some type of drill that incorporates both. On-field hitting would include an oppo round early but end with a more general "where it is pitched" round. Over time, recognition becomes more automated and the hitter can react properly to any pitch/location.