serratus activation?

Besides pushup plus type stuff, are there any good serratus activation drills?

 

I realized I wasn't getting full ROM on the planche progressions and I believe the left side serratus isn't turning on very well. I regressed back to kneeling scap pushups on my elbows and have to really give an extra push on the left to complete the motion. I believe this same issue is affecting my scapular position in other movements as well and might explain a lot of the shoulder problems I've had over the years.

 

I assume it's the serratus anyway. I have trouble activating the area along the ribs, under the armpit right about where the lat is but it's not the lat. I had a surgery in that area long ago so it might never be 100% but I'd like to do what I can.

 

Thanks.

1. Planche leans, if you protract and depress your scapula fully and contract your core muscles while maintaining a posterior pelvic tilt.

2. Scapula Depression and Elevation "Dips"(Youtube video)

I've been doing easier versions of the above exercises and I believe they're helping.

 

What's frustrating is that most of the muscles are strong enough to do things like dips and planche leans, I just can't keep the scapula tucked in and then the levator scapula (I think, it's some small muscle in the upper-trap/neck area) gets really tight and sore. It's only been in the last week that I've been able to get that muscle to chill out a little during certain types of movements. When that happens, I can feel more strain in the serratus area. It feels better and more 'normal' but is hard to do consistently.