A free throw shooter must stay behind the line until the shot reaches the rim. If you're having an issue getting the ball to the rim without stepping over, I'd recommend two things: 1) You could jump to provide power (possibly needing to start a little behind the line if you happen to jump forward or 2) Be sure to use your legs by bending your knees. Using your legs is one of the primary sources of power when you're shooting. Also, make sure your elbow's in. A crooked shooting elbow will reduce power.
Elbow in. Legs bent. One continuous motion upward.
Must be a young buck. just jump on em in games until you are strong enough to get em without jumping. there will come a time when you will be shooting around and try it and you can get it there no problem and you will be like wow i didn't used to be able to do that.
If you are young, then through time, you'll get strong enough to shoot FT's without jumping. I was able to shoot them without jumping when I was in MS. If you are older, it must be ore form. Andre Miller has a problem with stepping over after a freethrow and that's because his freethrow shooting form is horrendous. He doesn't use his legs and doesn't keep his elbow straight.