I do it as follows,
- set the CSS positioning for the applet to be absolute and off-screen
- enable the 'mayscript' applet property
- on completion of applet initialisation, call a Javascript function
- in that Javascript function, set the applet positioning to be static and on-screen, and any "please wait" elements to be hidden
Depends what you mean by "when asked to load/run the applet" - do you mean whilst the applet is loading?
In that case I'd make the Javascript event handler for the button set a boolean value, and in your Javascript function called by the applet on loading, check for it. So if the user's clicked cancel it won't change the CSS attributes to display it.