function OnClientFileOpen(oExplorer, args)
var item = args.get_item();
args.set_cancel(true); //this prevents the window from opening
var docLoc = "Handler.ashx?path=" + item.get_url();
document.location = docLoc;
That function is just a re-write of the one provided in the demo with all of the checking removed. It will force a download as well so perhaps you just need to use the args.set_cancel(true); line depending on your implementation.