From a conversation with Eli Faber:

> The only thing I have encountered is a description of how, in Jamaica, the Jewish slave owner gave his slaves all of Saturday (Shabbat) as well as Sunday off.  This was very significant because in Jamaica (I believe unlike in the eventual US), slaves were permitted to work parcels of land and sell the produce at markets.  Accordingly, the slaves of Jews were able to plant more, sell more, and earn more money than those owned by non-Jews, who gave their slaves only half a day off on Saturdays, as well as Sundays.  For my reference to this, as well as the source in which I found it, see the book I wrote, "Jews, Slaves, and the Slave Trade: Setting the Record Straight," page 62.   Jews in Jamaica thus adhered to the Biblical prescription that slaves, servants, etc., were to be able to rest on Saturdays, too; see the fourth of the  Ten Commandments ("Exodus," chapter 20).  The owners in Jamaica clearly adhered to this Biblical command---though the slaves reportedly chose to work on Shabbat.

Based on his extensive research into the matter, I think we can conclude that this was the extent that Jewish slave owners observed slave-related commandments in the Americas.