Create another data tiddler called UsHolidaysJson using the same data in a JSON format, and change your TodaysHoliday tiddler to look the holiday up in there instead. Everything should continue to work the same way on the transclusion side. The table looks like this in JSON:

{
  "01/01": "New Year's Day",
  "07/04": "Independence Day",
  "10/31": "Halloween",
  "12/25": "Christmas Day"
}