This might be a long explanation because I'm at work and can't snap a photo of what I'm describing since it's at home. When in Japan I bought one of those samurai sword letter openers and it came with a stand that holds in upright. You could make something similar out of wood. Let me try and describe it (minus dimensions). The base is flat with one hole/groove towards the back that allows the stand portion to "snap" in (this one is plastic but I think it would make a nice stand if made of wood). The stand portion is a straight piece of wood with the piece at the top that is widened and indented to allow the sword to rest there. I've included a very very rough sketch from MS Paint to help with the visualization.
If you put a few of the shells on one side of each, say 3 or 4 small ones and made a small pile with them it would look nice and not touristy but if you covered it with shells and coral then I think it would be a bit much. Hope this helps, if you need me to take a picture of the letter opener stand and post it I will.