Not able to set the value in RadNumeric Text box in OnBlur event

My requirement is - when user enter any number in the text box & tabout - i need to add leading zero's in the text box value.

                                              function AddPaddingToInvestmentNumber(sender, args) 
                                              {
                                  var textBoxVar = "<%=txt1.ClientID %>";
                            var fValue = $find (textBoxVar).get_value();
                          var resultset = FormatInvNumber(fValue, 5);
                        $find(textBoxVar).set_value(resultset);
                                            }

                               function FormatInvNumber(num, size) {
                                       var s = num + "";
                                  while (s.length < size) s = "0" + s;
                                                return s;
                                            }

code is working fine - but i am not able to set the value in radtextbox OnBlur event

    <telerik:RadNumericTextBox ID="txt1" 
      MaxLength="5" Type="Number" Width ="50"
      Font-Size="11px" NumberFormat-DecimalDigits="0"  
      DataType="System.Int32" runat="server">
     <ClientEvents OnBlur="AddPaddingToInvestmentNumber" /> 
     </telerik:RadNumericTextBox>

Try to set the sender -

          sender._value = yourvalue;
          sender._displayText = yourvalue;
          sender._text = yourvalue;
          sender._validationText = yourvalue;
          sender._textBoxElement.value = yourvalue;