Conditional Override of 'New' Button

Here is a VF solution expanding on Mark's comment. The fourth argument to URLFOR is nooverride

<!-- Display markup when running user is Switzerland, otherwise, use standard page -->
<apex:page standardController="Foo__c" 
       action="{!IF($User.Country__c = 'CH',
                    NULL, 
                    URLFOR($Action.Foo__c.New,null,null,true)
                   )}"

   <apex:form>
     <!-- my override markup goes here -->
   </apex:form>
</apex:page>