berg - ideally we shouldn't even be fishing and leaving them in peace but who the hell wants to do that? In all honesty, steelhead are tough as rocks, ever catch a fall fish? Those big minnow like buggers that fill the streams of up north lakes? Such fragile wimp fish. Think of stocked fish as little parr getting their fins clipped - the small little tiny squirmer is pulled outta the water, typically held with wool gloves until its fin gets clipped - out of water, slime getting stripped, scissors slicing and dicing yet they grow up to be majestic beasts.
Anyways, setting the fish down on the bank isn't great either - out of water for a while, flops around, slime gets stripped yada yada yada. I suppose the best, least intrusive way would be to keep it in a net and take a pic of it in the water or holding it by the tail in the water? Theres a good video pinned up top of a few of the subforums that one of our members found, check it out.