Fijate si te sirve algo así:
Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Documento sin título</title>
<script type="text/javascript">
function foo(){
alert('hola');
}
var cache={foo:window.foo}
</script>
</head>
<body>
<form action="" method="get"><input name="" type="checkbox" value="" checked="checked" onclick="foo=(this.checked)?cache.foo:function(){}" /><input name="" type="button" value="foo" onclick="foo()" /></form>
</body>
</html>