Maybe you should PM him and ask him if he'd be willing to post more, or see if he'll release the invasion forces into the public domain so any of the soldiers (except perhaps the commander) are controllable. They would add some drama to the heroes trying to find the bomb and annoying invasive forces getting in their way.
My idea was that Shelton and Kerzach sneak into the place where the bomb timer is located and, while they can't turn it off completely, can increase the timer from 30 minutes to 3 hours. They would also know the bomb hasn't been activated yet, and could radio this to James. Now James and co. have enough time to get back, and once they realize there's a chance Pelvanida could be saved, they take advantage of it.
Just an idea. I can't think of another reason why they'd turn around.