But the body is not required, remember Kelsier held Preservation in the time between Leras and Vin, Kelsier didn't have a body at that moment and if I could remember what chapter it preservation dies I'm 99.9% sure it says he was able to do so because he had chosen to not pass on to the Spiritual realm, therefore it was only the COGNITIVE aspect of him controlling the Shard.
Also I have confused Shardholder and Shardbearer on several occasions but that's just me