One of the way I know is duplicating image and resizing like %80 than adding huge gaussian blur like 200 pixel and add big curve for brighten midtones than resize the image again same size of your image and paste it top of your layer than you can add some levels ( something like bring the black slider to the middle ) than add
gaussian blur again blend it on screen mode like %40 opocity and warm up to image.. ( all of this process for creating a gradient with your light source )
but my personal opinion non of these work well and look realistic enough ..
best way to get this shoot wide open in the sun here some of my samples with natural way..
hope it helps a little