I’d suggest not using towels for HLR, just hang from the bar. You can resist the swing if you go more slowly. This control starts at the upper body, actively “push” the bar forward and down while focusing on the speed that your hips are moving, while also keeping your back and abs rigid.
For more abdominal work, I suggest working on building up time on L sits and also doing L pull ups. L towel pull ups are quite challenging!