Caranya mudah kok.tinggal ikuti sedikit langka-langka berikut:

1.Login ke blogger
2.Ke menu rancangan->Tambah Gadget->Gadget HTML/Javascript
3.Masukkan kode berikut
<script>
var message="Ganti Sesuka Kamu";
///////////////////////////////////
function clickIE4(){if (event.button==2){alert(message);return false;}}
function clickNS4(e){if (document.layers||document.getElementById&&!document.all){if (e.which==2||e.which==3){alert(message);return false;}}}
if (document.layers){document.captureEvents(Event.MOUSEDOWN);document.onmousedown=clickNS4;}
else if (document.all&&!document.getElementById){document.onmousedown=clickIE4;}
document.oncontextmenu=new Function("alert(message);return false")
</script>

Semoga Berhasil ya