I have 3 exercises up to now. I try to explain, but I find it hard, even in my mothertoungue, which isn't Englisch.
It's alsways advised of course to do both sides.
1. Go into slight lunge position, knee to train is front, knees bend according to what feels good, not more than 30 degree, because vastus medialis is most active within 0-30 degrees. Step or tap with the front leg without changing knee angle much. The harder and faster you step, the more the medials gets into action. knee must not be further than toes, knee must be in line with hip and foot. As soon as you can't maintain correct form stop. According to you ability adjust speed and force of stepping. Also adjust if you step with the back leg also or if you keep it to he ground. Also for the back leg of cource, knee must be in line with foot, as soon as you fel or see twisting, stop.
2. Same stance as above, leg to rain has again 20-30 degree angle, other leg is behind. Now you swing it in front and up, with knee flexed. As if you wana kick something, but without extending the lower leg. Swing back and touch the ground. Here also, according to you ability you can shift bodyweight to the back leg or have you bodyweight the whole tome on the supporting leg, which is the leg to train.
This exercise can made harder with an elastik band, loopes around your shin of the swingig leg (somewhere below the knee) and around lets say a table-leg.
3. Elastik band looped around table leg and hollow of the knee to train. Span the band nicely. slight lunge stance again, with the leg to train in the loop. Bend you knee foreward, again up to max. 30 depree and stretch it out again. Important again, knee must not be further than toes and always in line with toes and hip. if you shift you bodyweight foreward or choos a firm band it gets harder of course.
I startes with 20 reps each exercises (after that activation of he arthrosis), I saw medialisation of 2-3 mm within 2-3 weeks. Now I do 2 times 30-50 reps each leg each day. My leg has become stable again and I really can see there is something growning...
Also important to strecht the lateral patella lingament, by pushing the patella medial with you hand, when leg is stretched out.
Really, those exercises help me although I have trochlea dysplasia in one knee which is beyond words. Just todays I consulted a specialist für femoropatellar problems, THE specialist in this region or even in the whole of my country. Even he said he has not seen too much patients of this degree. And I have arthross, that's why I can't do leg extrension. I did lots of heavy stuff in the past, bevor arthrosis became so bad, but I saw myself, the outer part was growning and growning, but the inner part remained small.
Raising my bike saddle as much as possible helps a bit. Same effect, bigger angle in knee means more medialis action.
Also check out this guy: http://www.youtube.com/watch?v=q_x8A7lNGPY&feature=BFa&list=PL96454BD9C648C4B3&index=35
I did this training, except single leg squats (try thzem later again) and I think it helps me. I do it once or twice a week or so. Then from my old PT I got excercises on he balance board which support. Here again the supporting leg on the board always has this slight bend and that activates the medialis.