I did this, also with jQuery:
$('input[type=search]').on('focus', function(){
// replace CSS font-size with 16px to disable auto zoom on iOS
$(this).data('fontSize', $(this).css('font-size')).css('font-size', '16px');
}).on('blur', function(){
// put back the CSS font-size
$(this).css('font-size', $(this).data('fontSize'));
});
Of course, some other elements in the interface may have to be adapted if this 16px
font-size breaks the design.