Tomas
Here is some information on using custom page templates for single pages.
I think this is the only way you are going to get round this.
You will still be able to keep the centred formatting for the Blog title and menu stuff it is just the page width that will be modified since the page is white and there are no borders it should not matter.
Page Templates
Individual Pages can be set to use a specific custom Page Template (a PHP template file, e.g., snarfer.php) you create within your Theme (see Creating your own Page Templates below on how to create a custom template). This new Page Template will then override the default page.php Page Template included with your Theme. See What Template is used to Display a Particular Page? below, to find out exactly which Template will be used, but read the following first, so you understand the answer
WordPress can be configured to use different Page Templates for different Pages. Toward the bottom of the Write > Page administration panel (or on the sidebar, depending on which version of WordPress you are using) is a drop-down labeled "Page Template." From there you can select which Template will be used when displaying this particular Page.
NOTE: In order to access the Page Template selector, there must be at least one custom Page Template available in the active theme (see Creating your own Page Templates below to learn how to create one). If a custom page exists, but you still are not able to see Page Template selector, try to re-activate your current theme.
Here is link to wordpress site where I lifted the info.
http://codex.wordpress.org/Pages
Nigel