asp:TextBox - Is there a way to OnTextChanged working even after setting visible=false?

Is there a way to OnTextChanged working even after setting visible=false? I have a legacy asp page that has a number of postbacks and refreshes. I'm using this text box as a session variable since the equivalent variable in the code behind can get unexpectedly cleared during one of the many refresh events. This textbox can be changed because of a wanted ajax auto-complete call and I need to know when it does.

<asp:TextBox runat="server" Visible="false" ID="txtClientId" CssClass="text-box" AutoPostBack="True" OnTextChanged="OnClientIdChanged" />