Any thing added to your leader that is heavier or more wind resistant is going to foul up your casting. So do the best you can. Also try not using floating lines with long front tapers, they just make it worse because they are designed for delicate presentations. And look into right angle leaders. I think there is instructions for one in Deke Meyers book. Have used split shot for years in deeper holes (yes it sucks casting) for summer fish with good results. All this said I do prefer to swing a fly, but sometimes in certain places you cant get deep enough. Now I use bead heads, cone heads, or barbells on my flys to get down. A weighted nymph in summer (4s to 8s) can be a killer. And having fished with Jim Teeny years ago I know how good flys can be if presented deep and slow enough for Steelhead.