How to add an attribute to a method declared on partial interface?

using System;
using System.Net.Security;
using WCF = global::System.ServiceModel;
 
namespace CMAWCF.ServiceContracts
{
    public partial interface IMyServiceServiceContract
    {
        [WCF::TransactionFlow(WCF::TransactionFlowOption.Mandatory)]
        void DoSomething(CMAWCF.MessageContracts.RequestDoSomething
                             request);
    }
}

using System;
using System.Net.Security;
using WCF = global::System.ServiceModel;
 
namespace CMAWCF.ServiceContracts
{
    public partial interface IMyServiceServiceContract
    {
        //... More methods
        [WCF::FaultContract(typeof(CMAWCF.FaultContracts.DefaultFaultContract))]
	[WCF::OperationContract(IsTerminating = false, IsInitiating =
        true, IsOneWay = false, AsyncPattern = false, Action = "DoSomething",
        ProtectionLevel = ProtectionLevel.None)]
        void DoSomething(CMAWCF.MessageContracts.RequestDoSomething
                             request);
        //... More methods
    }
}

using System;
using System.Net.Security;
using WCF = global::System.ServiceModel;
 
namespace CMAWCF.ServiceContracts
{
    public partial interface IMyServiceServiceContract
    {
        [WCF::TransactionFlow(WCF::TransactionFlowOption.Mandatory)]
        [WCF::FaultContract(typeof(CMAWCF.FaultContracts.DefaultFaultContract))]
	[WCF::OperationContract(IsTerminating = false, IsInitiating =
        true, IsOneWay = false, AsyncPattern = false, Action = "DoSomething",
        ProtectionLevel = ProtectionLevel.None)]
        void DoSomething(CMAWCF.MessageContracts.RequestDoSomething
                             request);
    }
}