Android UI align button at the bottom of scrollview

I want to place a button of the screen in the below layout. The challenge is that there is a scroll view in the layout that does not have enough content to fill the parent. Here is the layout

<?xml version="1.0" encoding="utf-8"?>

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical"

android:weightSum="100" >



<ScrollView

    android:id="@+id/svAnsSum"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:layout_weight="100" >



    <LinearLayout

        android:id="@+id/llAnsSum2"

        style="@style/CodeFont.BlueText"

        android:layout_width="fill_parent"

        android:layout_height="fill_parent"

        android:orientation="vertical" >



        <TextView

            android:id="@+id/tvAnsSumHeader"

            style="@style/headerstyle"

            android:text="@string/AnsSumHeader" />

        <TextView 

            android:id="@+id/tvAnsSumBody"



            />



         <LinearLayout style="@style/bottomlinearlayout" 

             android:layout_gravity="bottom"



    >



   <Button

            android:id="@+id/bAnsSumConfirm"

            style="@style/buttonstyle"

            android:text="Confirm"

            android:enabled="true"



            />



</LinearLayout>





    </LinearLayout>

</ScrollView>

this is the button style

<style name = "buttonstyle">

    <item name="android:enabled">false</item>

    <item name="android:layout_height">wrap_content</item>

    <item name="android:layout_width">wrap_content</item>

    <item name="android:layout_gravity">bottom|center_horizontal</item>

    <item name="android:gravity">bottom|center_horizontal</item>



    <item name="android:text">Submit</item>

</style>

This is the linear layout style

<style name = "bottomlinearlayout">

     <item name="android:layout_width">fill_parent</item>

    <item name="android:layout_height">fill_parent</item>

    <item name="android:gravity">bottom</item>

    <item name="android:orientation">vertical</item>

    <item name="android:paddingBottom">40dip</item>

</style>