Add default width and height to image insert

Hi
I'm trying to add default width and height (say 320x280) to image insert, because my users are often putting really big images which are completely destroying the website's look.

How to change default bueditor image insert command code to have such a feature?

php:
$imce_url = function_exists('h') && imce_access() ? url('imce') : '';

return "js:
var B = eDefBrowseButton('$imce_url', 'attr_src', 'Browse', 'image');
var form = [
 {name: 'src', title: 'URL', suffix: B},
 {name: 'width', title: 'Width x Height', suffix: ' x ', getnext: true, attributes: {size: 3}},
 {name: 'height', attributes: {size: 3}},
 {name: 'alt', title: 'Text'}
];
eDefTagDialog('img', form, 'Insert Image', 'OK');
";