You could create a sheet with the "Reloading..." text and some stationary that is shown only during script execution.
However you should know also that it is extremely difficult to force QlikView/Windows to redraw the User Interface when something like a reload is running in the background. Close to impossible and - worst of all - unpredictable.
You could try with the "Opening Image" feature. See Settings->Document Properties->opening->Image which allows you to display an image for a number of seconds after opening the document.
The Progress Window however can only be suppressed by loading the document into a QlikView object through the OCX programming interface. The function call to (re)load the document has a switch to suppress the Progress Window. IT has its disadvantes too.