Michael,
There is no configuration for this but it would be pretty simple to do this filtering in the code.
Just go into the Print.js file in the Print widgets folder and replace line 219 with something like this:
Old:
this.layoutDijit.addOption(layoutItems);
New:
var new_layoutItems = array.filter(layoutItems, function(layout) {
//this is where you are filtering out what you don't want added
//or you do the opposite and only allow the ones you want to be returned
return layout.label !== "Letter ANSI A Portrait";
});
this.layoutDijit.addOption(new_layoutItems);