how to add controls to the masterpage's conten

On the base.master:

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Base.master.cs" Inherits="WebApplicationControlTest.Base" %>
<!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 runat="server">
    <title>The title</title>
    <asp:ContentPlaceHolder ID="head" runat="server">
    </asp:ContentPlaceHolder>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        There is a content here: <br />
        <asp:ContentPlaceHolder ID="body" runat="server">
        </asp:ContentPlaceHolder>
    </div>
    </form>
</body>
</html>

On the nested master

<%@ Master Language="C#" MasterPageFile="~/MasterPages/Base.Master" AutoEventWireup="true" CodeBehind="NestedMasterPageTest2.master.cs" Inherits="WebApplicationControlTest.MasterPages.NestedMasterPageTest2" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>

<asp:Content ID="PlaceHolder" ContentPlaceHolderID="body" runat="server">
    This is inside the NestedPage<br />
    <asp:ContentPlaceHolder ID="PlaceHolderLeft" runat="server">
    </asp:ContentPlaceHolder>
    <asp:ContentPlaceHolder ID="PlaceHolderRight" runat="server">
    </asp:ContentPlaceHolder>
</asp:Content>

and on the default.aspx

<asp:Content ID="PlaceHolder" ContentPlaceHolderID="PlaceHolderLeft" runat="server">
    This is a test!
</asp:Content>

on the default.aspx.cs

protected override void OnPreInit(EventArgs e){
    Control control = LoadControl("TheUrlOfTheControl.ascx");
    if (Page.Master.FindControl("body") != null) {
        Page.Master.FindControl("body").Controls.Add(control);
    }
}

I need to add the control to the last part of the body content Placeholder but FindControl does return null... how can we add controls to the masterpage's content placeholder programmatically?

Thanks

Answered for future reference

protected override void OnPreInit(EventArgs e){
    Control control = LoadControl("TheUrlOfTheControl.ascx");
    Control placeHolderControl = Page.FindControl("body");
    if (placeHolderControl != null) {
        placeHolderControl.Controls.Add(control);
    } else {
        MasterPage theMaster = Page.Master;
        while (theMaster != null) {
            placeHolderControl = theMaster.FindControl("body");
            if (placeHolderControl != null) {
                placeHolderControl.Controls.Add(control);
                break;
            }
            theMaster = theMaster.Master;
        }
    }
}