Use the "RallyEnumMultiSelectFieldHandler" in the "Connector" section. Here is an example:
Connector: FieldMapping: Field: - Rally: Name Other: Summary - Rally: DropDownListMulti Other: LoriDropDownMultiChoice RallyFieldHandlers: RallyEnumMultiSelectFieldHandler: FieldName: DropDownListMulti Mappings: Field: - Rally: Alpha Other: CH - Rally: Beta Other: CH2
The indentations in the example config above may not be correct. They should be 4 space indentations.