Following on from my previous post, it seems you require the really bizarre combo of F4, and THEN F3, in that precise order, to get full-screen stretch. A rather unintuitive combo, you should probably document that!! And I imagine it would still help if you could add an innate function for this.
For anyone else using this, I also managed to get debug working via:
Game_Temp.prototype.isPlaytest = function() {
return true;
};
Added as a small snippet plugin. Thanks to Gensun for help on this one.