Basta criar um drawable usando um InsetDrawable
<?xml version="1.0" encoding="utf-8"?>
<inset >="http://schemas.android.com/apk/res/android"
android:insetBottom="0dp"
android:insetLeft="-5dp"
android:insetRight="-5dp"
android:insetTop="-5dp" >
<shape>
<solid android:color="#FFF" />
<stroke
android:width="3dp"
android:color="#00F" />
</shape>
</inset>