class Customer
{
  Guid Id;
  CustomerData Data;
}
[Serializable]
class CustomerData
{
  // all the true false props. You can divide them into sub-classes for better organization.
  bool? IsMan;
  bool? HasDoneBusinessBefore;
  bool? IsNice;
}
lets say that the customer is a man and thats all you know about him now.
The DB will look like this:
Customer:
(id):
32462873423432423
(data):
<CustomerData>
  <IsMan>true<IsMan>
  <HasDoneBusinessBefore/>
  <IsNice/>
</CustomerData>
Your code has a Customer that was loaded from the DB.
Customer customer = LoadCustomerFromDbById(32462873423432423);// will deserialize the xml into the data property. 
now the customer has done business with you and you realized he isn't nice:
customer.HasDoneBusinessBefore = true;
customer.IsNice = false;
customer.Update(); //will serialize the data and update the db with the new xml. Your DB will look like this:

Customer:
(id):
32462873423432423
(data):
<CustomerData>
  <IsMan>true<IsMan>
  <HasDoneBusinessBefore>true</HasDoneBusinessBefore>
  <IsNice>false</IsNice>
</CustomerData>
Now adding new properties will happen only in the customerdata class(no updating the db here).
Since the properties are "nullables" you can add them without giving default values that you dont want to give.
A good example is with the IsNice property. The customer hasn't done any business with you. That doesn't mean he isn't nice.That means you don't know if he is and you will update it on a future transaction.
Adding a new customer is adding a new row into the customer table.