Not in a manner that will work across browsers. You could, however, do that with some relatively trivial Javascript..

function makeCasesClickable(){
    var cells = document.getElementsByTagName('td')
    for (var i = 0, cell; cell = cells[i]; i++){
        if (cell.className != 'case') continue
        var caseId = cell.innerHTML
        cell.innerHTML = ''
        var link = document.createElement('a')
        link.href = 'http://bugs.example.com/fogbugz/default.php?' + caseId
        link.appendChild(document.createTextNode(caseId))
        cell.appendChild(link)
    }
}

You can apply it with something like onload = makeCasesClickable, or simply include it right at the end of the page.

HTML

<a href="whatever.html" class="more">More</a>

CSS

body {
    font-size: 12px;
}

a.more {
    font-size: 11px;
}

No. Its not possible to add link through css. But you can use jquery

$('.case').each(function() {
  var link = $(this).html();
  $(this).contents().wrap('<a href="example.com/script.php?id="></a>');
});

Here the demo: http://jsfiddle.net/r5uWX/1/