How to make a logo wrapper of 100%

[gjh42]

You might be able to do it using some custom javascript. If so, you should be able to find info on the process by googling on js code sites.

But think about what you really want. Does the image want to stay the same height? If so, the letters or images on it would get distorted as the header gets wider or narrower. If you want the image to stay proportional, it will get taller or shorter depending on window size while the rest of the page stays the same scale.
You might look at the CSS "sliding doors" technique for getting a header that fits a fluid width.