SAP Hybris Commerce - Initialize default value for a reference attribute

I'm working on SAP Commerce (Hybris) 1811 and I'm trying to extend a Product type with a reference to a type ProductSales, which is going to contain product sales data and be filled via a cronjob.

However, I can't find a proper way to initialize this new type for all new and existing products. Even after a system update, this reference is uninitialized (null).

There should be a 1-to-1 relation between Product and ProductSales.

I'd like this referenced type to be initialized:

1. During system update for all existing products which don't have the reference yet
2. Create an instance for all newly created products

My items.xml definition:

<itemtype code="ProductSales" autocreate="true" generate="true" >
    <deployment table="productsales" typecode="15011" />
    <attributes>
        <attribute qualifier="unitsSold" type="localized:java.lang.Long">
            <description>Amount of units sold</description>
            <persistence type="property"/>
        </attribute>
        <attribute qualifier="ordersCount" type="localized:java.lang.Long">
            <description>Count of how many orders contained this product</description>
            <persistence type="property"/>
        </attribute>
    </attributes>
</itemtype>

<itemtype code="Product" autocreate="false" generate="false">
   ...
    <attribute qualifier="productSales" type="ProductSales">
        <description>Product Sales</description>
        <modifiers partof="true" optional="false" initial="true" />
        <persistence type="property"/>
    </attribute>
   ...
</itemtype>

The reason I'm not storing the data directly in the Product table, but as a reference, is that I don't want these data to be synchronized during catalog synchronization.

What would be the best way to initialize this new type for all products?

Thanks for any tips.

In the end, I solved this by creating the missing references in the cronjob itself. I only create this wrapper object in the staged catalog to be synced later.

By the way, I found that besides modifying the sync job, creating a wrapper object and keeping its reference synchronized between the catalogs is the solution recommended by SAP.