Doctor stoppage - I did it this way, and got it on my first try.
Make a career mode fighter but don't use him at all so he has 0 in standing strikes defense and clinch defense. Go to exhibition put beginner and 5 rounds fight against your career mode fighter with a ufc fighter with good clinch striking. (I used Wand) Then clinch and push the CAF against the cage and just keep pressing Y (Don't do a strong punch you'll KO him) and eventually the doctor will come in to check the cut. Just continue doing what you were doing and he'll stop the fight.
Flash KO - I picked Carwin and used a CAF with no striking defense and used Carwins strong punch and ko'ed him. Took a few tries though.
Basically for all of them just use a crappy CAF. For TKO & Sub just work the body a ton and eventually they'll get rocked then you can finish and repeat and get the sub.