I personally dislike that stretch... not for any particular reason, it just... doesnt seem helpful...
You need to learn to relax, and let your body do its thing.. middle splits will come when you can allow your body to gain the proper range of motion - which comes from training your hips, tendons, and muscles to stretch in that particular way.
Many of us coaches have discussed how to best stretch, and a few articles have been written to explain what the best methods are - a lot of them dont agree...
The best results I have gotten always are those that come with natrual progression, and what I think is plyometric stretching (my terminology on it all is weak, but the method works). Basically, do your middle splits to a point that you have a comfortable stretch. Squeeze the muscles that you feel stretching for 15-25 seconds (some coaches say 30). It's HARD!! And that's ok. Keep that squeeze going. After that time, relax. You should sink a little further lower towards your split comfortably. I usually repeat the process 3 times in one attempt.
It is also well known that your muscles are more responsive to stretching after a good work out. So, you can work your splits before practice, and again right after your conditioning routine.
You can work flexibility at home by stretching while watching TV or doing homework. Point your toes, and keep in a stretch for a while. About 3 minutes a position would be ok. You dont want to stretch too far for too long. It comes with the natural perk of keeping your toes pointed naturally. Yay!
Shoulder stretches are tough... every day, take a towel or a broom stick and stretch as far as you can over your head, from behind (like handcuffs) and pull up, lean against a wall and stretch, practice eagle (dorsal)
grips... just like your middle splits - keep it safe, and dont push past your comfort zone. Bridges, back walk overs, front walk overs, and front limbers will help your shoulders too.
Im sure others will put in their two cents... the approach to this is as variant as there are coaches, but they all focus on the same concept - be safe, dont push too far, and go slow so your body learns.
Good luck!!
Ryan