Oh Farmer how well I know that feeling, the hard lump in the stomach, the inability to really look him in the eye any more. The lump in the throat when he rolls over for a belly rub. There is no easy answer, just do it quickly.
All my pigs love the sun, spend a lot of time in the mornings liberally applying sun tan lotion to the ears then spraying with after sun in the evenings. They have shade, wallows, trees all of which they utilise. One of mine managed to get sunburn on her belly.