Answer:
   
   Although there have been demonstration Seders at a goodly number of
   Christian churches, the key word is "demonstration". These are
   educational experiences, rather than observances. Note that there is
   no historical basis for the assumption the the Last Supper was a
   Seder.
   
   Note that the Seder states "We do this because of the Eternal One did
   for US, when he led us out of the land of Egypt." The Seder can not be
   separated from Jewish peoplehood.