Retrieve additional user properties from ActiveDirectoryMembershipProvider - asp.net

Question

The ActiveDirectoryMembershipProvider in ASP.NET returns users as instances of MembershipUser. This class only returns two of the properties defined for the given user in AD: email and username. I need to get access to additional properties, specifically "DisplayName", as I need to show full names in a dropdown in a web form.
The only way I can find to do this, is via a separate connection to AD, along the lines of what is described here: How can I convert from a SID to an account name in C#. This seems like a cumbersome and inefficient solution. I would like to do something like membershipProvider.GetUserProperty(username, propertyName), but that's not available.
Are there any nice solutions that people know of?

Answer 1

Based on feedback from my colleagues (thanks, Eirik!), #KennyZ's comment and lots of Googl'ing, I have found that this is the best/only way to do it. For reference, and other people seeing this question, here is some useful code for getting the AD settings out of web.config+connectionStrings.config, and using that data to query AD for a given user's Display Name:
var membershipSection = (MembershipSection)WebConfigurationManager.GetSection("system.web/membership");
var providerSettings = membershipSection.Providers["ActiveDirectoryMembershipProvider"];
var connectionStringName = providerSettings.Parameters["connectionStringName"];
var adUser = providerSettings.Parameters["connectionUsername"];
var adPassword = providerSettings.Parameters["connectionPassword"];
var adConnection = WebConfigurationManager.ConnectionStrings[connectionStringName].ConnectionString;
var adReference = new DirectoryEntry(adConnection, adUser, adPassword);
var search = new DirectorySearcher(adReference) {Filter = string.Format("(mail={0})", username)};
search.PropertiesToLoad.Add("displayName");
SearchResult result = search.FindOne();
if (result != null)
{
var resultCollection = result.Properties["displayName"];
if (resultCollection.Count > 0)
{
var displayName = resultCollection[0].ToString();
...
}
}
Note: This assumes that I am using userPrincipalName as the attributeMapUsername in web.config, as that maps to the user's email address.