Thanks to kloudie1, JamesG, and rgranger, who actually answered my question, and suggested trying mineral spirits. My small test sample worked so we thinned the rest of our paint with mineral spirits and finished the job. Thinning more would have probably improved brush-ability but we decided not to dilute the ePaint any more than necessary.
We finished painting Friday afternoon and when we launched Sunday morning the paint was still on!!
We finished painting Friday afternoon and when we launched Sunday morning the paint was still on!!