If I have a student trying to break the wedge, let's go on easier terrain than they normally ski. Having them follow in my tracks using the narrowest wedge they feel comfortable with, we start with large radius turns, funneling down to shorter, more rhythmic turns. If the student has good fundamental balance, once we get to the shorter turns, the majority of the time I see the skis spontaneous match at or right after the fall line, and they don't even realize it's happening! When I point it out, the student gets pretty stoked and the the hurdle of getting parallel becomes much smaller. After that it is just refining those movements and sensations and getting mileage.
I like to start with drills that will put the skis parallel and get us comfortable on corresponding edges. So in a traverse we are marching across the hill (pretty hard to march in a wedge), using the up hill edges of our skis to push off the snow, back and forth. Progress to jumping in the traverse, pushing off and landing on the uphill edges (while maintaining a good stance/balance). Back and forth, back and forth. After that I like to move to drills that start guiding pressure to outside/downhill ski. So in traverse, tap the tail of uphill ski while pressuring big toe edge of downhill ski, back and forth. Then try to see if they can lift the up hill ski in a traverse and for how long, while pressuring big toe edge of down hill ski (this will also give you a good idea of where their balance is. Is the ski tip higher than the ski tail? Are they able to shift balance laterally to stand on the downhill ski?). Back and forth, back and forth getting practice.
After that, I'll take them back to tapping the tail of the uphill/inside ski, but with a challenge! Can they start tapping right after the fall line? Sooner? In the fall line? We'll go back and forth, trying the start tapping the tail of the inside ski sooner and sooner. Can we do it through the whole turn? After that, let's do another follow the leader. Are the skis now matching through the turn? Usually yes! After that we can work on getting a ton of mileage with our parallel turns. Let's see if we can increase our speed and keep parallel, increase pitch, or even get in the crud and stay parallel.