VS 2005 : User Settings Metric/Imperial XMLserialize?

I am having a bit of an issue and would like some opinions. I have a settings class that I use in my program that gets passed around to various pieces of the program. When the program exits, the settings class is serialized out to an xml file. When the program starts the settings class is serialized back from the xml file.If the program doesn't find an existing xml file, the defaults in the class are used and a new xml file is created when the program exits.This all works well. Here is a trimmed down version of my settings class:

Public NotInheritable Class UserSettings
Private _Length As Double = 10 'feet
Private _Name As String = "Inert Material"

[code]....

The problem that I am having is that if the program units are metric, then the default values are always converted in the constructor and the xml serializer then stuffs the values that exist in the configuration (over writing the converted default value which is what I want) into the proper properties. The reason for this behavior is to make sure that that new properties that don't exist in the xml file have a proper default value when metric units are required.

It seems wasteful to convert all of the default values every time when working with metric units? Is there a better way to do this? My full class has currently about 15 default values that need to be converted to metric equivalents. Ideally I would only like to convert values that haven't come from the xml file.