The good news is that Tableau has committed to making Tableau's web editing feature equivalent to Tableau Desktop in 2017. The bad news is that it's not 2017 quite yet and we don't know when parameter editing will land as a feature.
The only workaround I can think of would be to use a Tableau data blend to enable to the sort, this is a variation on Creating a Dynamic “Parameter” with a Tableau Data Blend | Drawing with Numbers and you'd need to build out a custom calculated field to put as a discrete field on Columns or Rows to get the sort since you can't do a pill sort based on a secondary source. If you have questions about how to do that let me know and I can set up an example.
It's now almost 2019 and the parameters are still not supported in Tableau Online