Probably the easiest way is not to query the data source when the form opens.
On your data connection one of the last options you get to set is "'Automatically retrieve data when form is opened' Note: Your form will open [sic] more quickly if you delay data queries until the data is needed. To do this, create a rule to query data hen a button is clicked or when the value of a field changes."
Untick this box.
You now need to manually query the data source which you do from your button.
if you need to filter the data source then set one of the QueryFields on the data source prior to retrieving data.