Hi! This seems like a strange drill because it involves letting go of the bar, but IT WORKS because it gives the gymnast the "feel" of the front hip circle ... as in the momentum required for the skill.
From a front support on the low bar, have the gymnast press down on the bar so her thighs rise. She should fall forward, let go of the bar quickly with both hands, and immediately grab the back of her thighs, right above the back of her knees. (Her legs will need to be tucked after the initial fall forward). She will circle around the bar to the top, and her arms/shoulders/hands will end up over the top of the bar. She will need to re-grasp quickly.
Sometimes, girls are scared to let go of the bar, so I recommend spotting this drill at first. Once the gymnast understands where she must grab her legs to complete the circle, she will feel comfortable doing it! And once she gets this drill down, she will be much closer to completing a regular front hip circle, since understanding the momentum is so important in mastering this skill.
Have the gymnast on the bar in a front support, coach in front of them. Keeping straight arms have the gymnast fall forward, their legs should remain straight and move upward as lower body moves down. They should be moving like a see-saw, staying straight as they fall forward, past horizontal. The coach has their hands open so their shoulders come into contact with the palm of their hands, giving a slight push on them to pop the gymnast back into a front support. This helps them to not pike early and teaches them how to adjust the tightness of their grip to complete the up/down motion smoothly.
I like to start these drills as soon as the gymnast can do a front support with the bar on the thigh, tummy in, and straight arms with shoulders down. For some that's sooner than a pullover! Even if they can only get popped back up 2 or 3 times with good form. One thing I dread is having a to fix a front hip circle that's done with such a hard pike that the gymnast is wrapped around the bar. Since they can get all the way around, making a change is extremely hard. Teaching them to fall past horizontal straight as early as possible minimizes the chance of the wrap-around once they are ready for the full skill.
I tried MilaElizabeth's drill yesterday with my level fours, most who have their front hips, but a few do not. I am very excited about it! The girls LOVED doing it- thought it was totally fun. The ones that had it already were working on fixing their bent knees because they could actually see and feel it since they were grabbing their legs. The ones that don't have their front hips got SO CLOSE in just one day of doing the drill. I love it. Thanks!