Using boto to create a AWS data pipeline for the RedShiftCopyActivity

I am trying to move data from s3 into redshift and want to enforce uniqueness on primary keys in redshift. I realized that the copy command itself can't do this. However, I noticed that the RedshiftCopyActivity available through the AWS data pipeline allows an "OVERWRITE_EXISTING" flag which would allow an enforcement of the primary key in some way at least.

I was wondering whether boto could be used to achieve this and if someone could point me to an example of such a use.