Could you put a shelf on the wall above the fireplace? Maybe a thick hand hewn looking board with simple supports that would be sort of like a mantle. Their are building codes that set distances from the fire opening and fire box to combustable materials. If you know who the manufacturer of your fireplace is they can probably help you. If you can't find out who the manufacturer is a good chimney sweep may be able to give you some advice. Metal fireplaces and flues should be cleaned at least once a year anyway (we learned this the hard way--chimney fires provide a little too much excitement.) so you should have the opportunity to talk with a sweep. When you do don't forget to shake his hand.
"Christmas stays if we don't forget its meaning"