A couple of questions. Is there enough clearance that the face and skirt of the hammer will fit over a cap placed on the nipple? Is the skirt thick enough that you can grind a little off the inside of the skirt to give you clearance?
If the answer to either question is " Yes ", then I would not be moving that hammer away from the lockplate any with spacers. It is really not that hard to heat the nose of the hammer up and bend it a little. You do want to make a template of the before and the intended after location so you can campare what you have done with the template while the hammer is still hot. A gunsmith should be able to bend the hammer for you, but if you have access to a machine shop, a hammer, and anvil, or something similar, you should be able to do it yourself. When you do heat the hammer up, and bend it, do not quench it in water or oil. Let it cool down slowly so it remains soft. It does not have to be hardened to do its job. Het to a cherry red to bend it. Some use a good wrench or vise-grips pliers to do this kind of bending, instead of a hammer, and anvil. The bend is going to be so slight, that either works. You will have to grind metal off the face of the hammer so that you get an even contact between the hammerface and the top of the nipple. Use napkins, or paper towel to test the contact, and not cardboard. Its too thick and you cannot see the subtle differences in height. Use a small grinding bit in a dremel tool to grind off the high spots on the face of the hammer.