This is my attempt to create a custom brush to simulate the brokeh of a SLR lens.
1. on a new image, created a octagon shape, fill with black and save as a brush.
Select settings to scatter, wet edges, vary opacity and size
2. Open image with "ordinary" background
3. Duplicate background layer, gausian blur to achieve out of focus background
Add layer mask and mask the subjects that are to be returned to focus
4. Create new layer and use the "brokeh" brush to create highlights over apprpriate light areas.
Reduce opacity of layer to liking and apply a small amount of gausian blur if desired.