Updating weakly typed properties in Orders

Hi folks!

I'd like update some weakly typed properties in my orders. I'm using the 
OrderServiceAgent through the OrdersWebService.

I have success updating "native" properties using the method:
OrderContext.PurchaseOrderManager.UpdatePurchaseOrderProperties(...)

<PurchaseOrderUpdates>
    <PurchaseOrder
        OrderGroupId="df20946b-b2c2-4d27-b6ba-e3b6133f4110"
        PropertyName="Status"
        PropertyValue="UpdatedOrder" />
</PurchaseOrderUpdates>


But I cannot found a example to update weakly typed properties. I did try
a 
lot of ways without success. Can you help me?


[],
Queiroga