If they are required you need to add them. You would have to manually add these in any case.
However since you are doing a POST here in a GetRows the data it expects is a JSON Object, so you could use a dynamic object instead of a dictionary.
Something like this
var myPostdata = new {
whereClauseLaborHed = "Your Where Clause here",
whereClauseLaborDtl = "",
whereClauseLaborDtlAttch = "",
whereClauseLaborDtlComment = "",
whereClauseLaborEquip = "",
whereClauseLaborPart = "",
whereClauseLbrScrapSerialNumbers = "",
whereClauseLaborDtlGroup = "",
whereClauseSelectedSerialNumbers = "",
whereClauseSNFormat = "",
whereClauseTimeWeeklyView = "",
whereClauseTimeWorkHours = "",
pageSize = 0,
absolutePage = 0
};
EpicorRest.DynamicPost("Erp.BO.LaborSvc", "GetRows", myPostdata);