Beginning with R2016b Simulink Data Dictionaries can store time series objects in the 'Other Data' dictionary section. For Example:
dicth = Simulink.data.dictionary.create('MyDictionary.sldd');
otherh = dicth.getSection('Other');
myTimeSeries = timeseries;
otherh.addEntry('myTimeSeries', myTimeSeries);
open('MyDictionary.sldd');
Note: this does not work in previous version of Simulink or in other sections of a Simulink Data Dictionary.