The Magistrates' Court decision that originally approved the extradition seems to state that it would be strictly harder:
> If Mr Assange is surrendered to Sweden and a request is made to Sweden for his extradition to the United States of America, then article 28 of the framework decision applies. In such an event the consent of the Secretary of State in this country will be required, in accordance with section 58 of the Extradition Act 2003, before Sweden can order Mr Assange’s extradition to a third State. The Secretary of State is required to give notice to Mr Assange unless it is impracticable to do so. Mr Assange would have the protection of the courts in Sweden and, as the Secretary of State’s decision can be reviewed, he would have the protection of the English courts also.
> If Mr Assange is surrendered to Sweden and a request is made to Sweden for his extradition to the United States of America, then article 28 of the framework decision applies. In such an event the consent of the Secretary of State in this country will be required, in accordance with section 58 of the Extradition Act 2003, before Sweden can order Mr Assange’s extradition to a third State. The Secretary of State is required to give notice to Mr Assange unless it is impracticable to do so. Mr Assange would have the protection of the courts in Sweden and, as the Secretary of State’s decision can be reviewed, he would have the protection of the English courts also.
http://www.judiciary.gov.uk/Resources/JCO/Documents/Judgment... , page 28