Do it in post. In PhotoShop, what I like is creating a duplicate layer set to "screen," using "select by color" or levels command to isolate the bright things, apply a little gaussian blur to that and adjust the layer's visibility to suit. I hadn't had a similar problem with Aura the one or two times I tried it, tho. Check if you can ramp up the "Quality" on the effect -- I think there's a slider.