pager.ascx

public partial class pager : System.Web.UI.UserControl
{

}

.aspx

protected pager ctl;

protected void Page_Load(object sender, EventArgs e)
{

ctl = (pager)this.LoadControl("controls/pager.ascx ");
ctl.ID = "c_page";      
gvwList.BottomPagerRow.Cells[0].Controls.Add(this.ctl);  

}