Map value from csv file to enumeration list

Hi,

When importing a work item from csv, how does one get a value to appear in an enumeration list? We are migrating a field called "Customer  Name." In RTC, the corresponding field (with an ID of "customers") is an enumeration list, which is backed by the CustomerName enumeration. We have a customer called "CustomerA." The ID of said customer (in the enumeration) is customer_name.literal.l23. The CSV file also reads "CustomerA." I have tried:

<attribute sourceId="Customer Name" targetId="customers">
<value sourceId="CustomerA" targetId="customer_name.literal.l23" />
</attribute>

and

<attribute sourceId="Customer Name" targetId="customers">
<value sourceId="CustomerA" targetId="CustomerA" />
</attribute>

I would expect one of these to cause "CustomerA" to appear in the work item, but no customer name ever appears in the field. Is this a supported field type for migration? I am using RTC 4.0.1.

Thanks,
- Josh