Youc could consider to use Value Stream to store your data.
After you successfully discovered Tags in your KEPServerEX Thing, You browse the Tags in Kepware from KEPServerEX Thing, and then you bind it to a New Thing with "Bind to New Entity", and this new Entity is based on IndustrialGateway Template, and also remember to set a Value Stream:
Set the bound Tags which you want to show in mashup with "Logged".
And then you bind QueryPropertyHistory in the new kepware Thing in your mashup, and bind the Returned Data to Time Series Chart. To get refreshed periodically, you could add a Auto Refresh widget in your mashup.
Hope this helps,