Public read-only properties

[mat]

Assume I have a business object that has some properties that should
be read-only. For example:

public class Order
{
...
public DateTime OrderDate { get; set; }
...
public decimal OrderTotal { get; set; }
}

Also assume that OrderTotal is a calculated value returned by a stored
proc that cannot be set by the application (whereas OrderDate can).
Normally I would simply write the OrderTotal without a public setter:

public decimal OrderTotal { get; private set; }

However if I do so BLToolkit will no longer set the value of this
property. I also already tried to write this as an internal property
and defining BLToolkit as a friend assembly
(InternalsVisibleTo("BLToolkit.4, PublicKey=xyz")) with no success.

How can I write a property without a public setter that can still be
populated by BLToolkit?

Any help is appreciated.

Thanks,
Mat