It is not possible but you can make it with a little tip
If your dessigner divide the icon in two parts, in this case, the top of the Droid and the legs of the droid and you add this legs to the Activity layout with a ImageView/View you can simulate the effect of the bigger icon.
The unique problem is the icon padding but i think you can set to 0. Perhaps its more easy if you use the ActionBar Sherlock library and change the code (its open source) ActionBar Sherlock and the ActionBar native are equals