preload CheckedImageUrl for ToggleButtonExtender?

hello

how can i preload the checked image, CheckedImageUrl, for a ToggleButtonExtender connected to a asp:CheckBox control when the page is first served to the client so that when the user clicks on the checkbox it doesnt flicker. i can see in fiddler that the flicker occurs the first time the checked image is requested. any ideas?

<asp:CheckBox ID="RememberMe" runat="server" Text="Remember Me" CssClass="login_chkRememberMe" /><cc1:ToggleButtonExtender ID="RememberMe_ToggleButtonExtender" runat="server" CheckedImageUrl="~/Images/chkbox_checked.png" Enabled="True" TargetControlID="RememberMe" UncheckedImageUrl="~/Images/chkbox_unchecked.png" ImageHeight="17" ImageWidth="18"></cc1:ToggleButtonExtender>

thanks

zaint [:)]