What I have done for autofocus on targets with few stars in the field is to find an area near the target with a good number of stars and create a sequence using the Faming and Mosaic wizard. I then slew to and center on this target and run my initial autofocus. You can then set it as the focus position. I had great success with my SCT to autofocus for each filter (wide and narrowband) on an open star cluster. After setting the focus, I then slew and center on the target, set the camera rotation, and then calibrate PHD2 on a guide star. With target and focus positions set, then autofocus will work flawlessly for me. After initial focus on the star cluster or area with enough stars, good focus is achieved and refocusing on the target is usually successful, provided the transparency and seeing are sufficient, even with few stars and with Ha or Sii filters. No plate solving needed other than for recentering.
To automate the sequence, you can move the focusing sequence to the top of the list, set the camera rotation to that of the target, do the autofocus and let the camera reach set point, take one exposure to save the HFR on the imaging binning setting, then move on to the first imaging target.