I don't think you can have multiple adsense accounts on one website according to the Terms and Conditions of Google Adsense.
Quote:
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You agree that while You may display more than one (1) Ad Unit on each Site Web page, You shall not display any Ad Unit on a page that contains Ads associated with another Google adsense customer (e.g., Your Web hosting company), unless authorized to do so by Google or such other adsense customer, if authorized.
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