How to take ASP.NET apps offline?

I have around 5 different ASP.NET apps that utilize a single database. A couple of times a week, I need to run some DTS packages to updates the database that all the apps use.

So, I have created a simple table that has a IsDatabaseOnline field which is of type bit. So setting this to 1 could imply yes and a 0 could imply false.

So in each on my app, I check for this value which redirects a user to a Site Down page if the data base is offline.

Right now, my approach is to create a base class where I have the following:

public class LaunchPadBasePage : System.Web.UI.Page
{
    private LaunchPadUser verifiedUser;

    protected override void OnLoad(EventArgs e)
    {
        if (!IsPostBack)
        {
            if (!SiteStatusBLL.IsSiteOpen())
                Server.Transfer("SiteDown.aspx");
        }

        base.OnLoad(e);
    }
}

All my .aspx pages inherit from this base class  something like
public partial class _Default : LaunchPadBasePage

Here is my question: since all my .aspx pages inherit from this base class, each time a user hits a page, the app checks for the IsDatabaseOnline field to determine if the site is offline or online.

Here is what I want to accomplish: I want to check for this value from only some of pages and ignore checking for this from the rest of the pages. So, I guess I need a way to move it from the LaunchPadBasePage base class.

You might say, simply dont inherit from this base class. But I have other things going on in the base class that all the pages need access to.

So, my question is, whats the best way to accomplish this?

Is there something in Global.asax that I can utilize?

I tried to place this code inside the Session_Start() method, but it looks like Session_Start() is called just once  when the user visits the website the first time. So this approach does not work.

I know you can place the app_offline.htm in your app to take it offline, but I will need to do this for 5 different apps every time I want to run the DTS packages.

Any advice?