This is probably the most common way the average student starts using an omoplata, and might well be the first entry into omoplata that you use successfully while rolling. When you have setup a basic triangle choke, one common way to defend is to keep the arm hidden underneath, not allowing the "hips up, arm over" step to happen. From here (assuming your partner is hiding their right arm under your hips), your main objective is to get their head over to the other side of their body, away from you. There are three basic ways you can accomplish this.

First, you can simply push away with your hips to create space. Second, you can push with the palm of your hand, creating room for the following step. Finally, if you're flexible enough, you can simply bring your left foot in front of your partner's face. Ultimately, this is what you want anyway. Once you're here, it is often useful to use your right leg to push your partner's face away further. Next, hug your partner's hips so that they don't roll to escape. Now you have the omoplata setup.