There are two simple steps to create a custom cancel button:
Example 1:
<CuteWebUI:Uploader ID="Uploader1" runat="server" CancelButtonID="Button1"></CuteWebUI:Uploader>
<asp:Button ID="Button1" runat="server" Text="CustomButton"/>
Example 2:
<CuteWebUI:Uploader ID="Uploader1" runat="server" CancelButtonID="Image1"></CuteWebUI:Uploader>
<asp:Image ImageUrl="~/Uploads/myImg.gif" runat="server" ID="Image1" />