How to read configuration in chaining method AddNServiceBus after adding configuration from vault?

Question

I have the following code to set up my application:

var hb = new HostBuilder()
.ConfigureAppConfiguration((hostConfig, build) =>
    {
        build.SetBasePath(Environment.CurrentDirectory);
        build.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);
        build.AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT")}.json", optional: true);
        build.AddEnvironmentVariables();
        build.AddVaultConfiguration((builder, config) => VaultConfigurator(builder, config));                   
    })
.AddNServiceBus(configuration, GetSpec(), disableStrongMessageType: true, nsbTransportKey: connectionStringKey)

What I need to do is read the updated configuration in the chained method AddNServiceBus(). I need to do this because at runtime we are reading values from a vault build.AddVaultConfiguration.