Can you do standing BHS BHS? If so, I'd start with rows and rows and rows 2-3 BHS from a stand.
If not, do standing BHS to stick with no rebound, land with head down, hands in front of your knees, and freeze it there. No rebound, no steps, nothing. Then without moving your feet or swinging your arms past your knees, do another standing BHS from that position.
Do that same thing a million times, and eventually you'll find the pause between them gets shorter and shorter until it eventually becomes a full connection.
Then we add the roundoff in. Start by doing it from a knee lunge, stick in the same position described above, and standing BHS. Then connect them. Then do the RO from fall-step. Then from one step and a hurdle. Then two steps and a hurdle. Then three, and you're good to go.