Letter Template - Linked records

Hi there.

I am setting up a series of letter templates at the moment and having some trouble.

Each of our customers is linked to a Partner.

On some of these letters, I need to use just the Partners first name.  I am able to get the Partners full name as this is shown on the Customer record but cannot source the first name on it's own.

On the partner record, of course, the tag for first name is < NLFIRSTNAME > which obviously does not work as it will give me the current record (the customers) first name.

The only way I can currently think of to get around this is to have a field for "PArtner First Name" on the customer record.  I don't want to do this for a number of reasons - it's messy and I'm not even sure how I could source (again!) just the first name!  I don't want reps to have to enter this value when setting up a partner or customer.