Dynamic Update The Data Using EF4 In Mvc

for example, i have a data table named [User], and mapping to User enetity with EF4: Id, FullName, EmailAddress, Fax, Tel in the web page, i just only want to update the "EmailAddess" and "Fax" 2 properties below:

@using (Html.BeginForm("Edit", "User"))
{
<label>Email Address:</label>
@Html.TextBox("EmailAddress")
<label>Fax:</label>
@Html.TextBox("Fax")
<input type="submit" value="Update" />
}

and controller i did for this:

public ActionResult Edit(User user) {
var _user = GetUsers().Where(a => a.Id == user.Id).SingleOrDefault();
_user.Fax = user.Fax;
_user.EmailAddress = user.EmailAddress;
context.SaveChanges();
}

yes, i updated it and successful, but next time i also want to update "Tel", so i need to change the code like this:

_user.Fax = user.Fax;
_user.EmailAddress = user.EmailAddress;
_user.Tel = user.Tel;

if i have 100 fields, i will be crazy for doing it :( So, how can i only update the models to database for related fields in web page?