how to use multi member ship provider in web config and on page

HI,

i want to switch membership provider if necessary after login button click.

i have added two in web config as below.

  <add name="AspNetSqlMembershipProviderOnLine" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServicesOnline"
             enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false"
             maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10"
             applicationName="/" />
          <add name="AspNetSqlMembershipProviderOffLine" type="System.Web.Security.SqlMembershipProvider" connectionStringName="ApplicationServicesOffline"
              enablePasswordRetrieval="false" enablePasswordReset="true" requiresQuestionAndAnswer="false" requiresUniqueEmail="false"
              maxInvalidPasswordAttempts="5" minRequiredPasswordLength="6" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10"
              applicationName="/" />

please detail advice, thanks