Populate default invoice template from project billing

Summary:

Our client has short and a long invoice template for each country. The bills are generated from project billing and we are intending to store the default AR invoice template in contract lines or customer master depending on which object can be used for automation. 

I read in one of the forums that BILL_TEMPLATE_NAME field in ra_customer_trx_all need to be populated for the print invoices program to pick the appropriate template whilst printing invoices in Receivables.

Does anyone know a feature that can be used so that when an invoice is interfaced from project billing to AR and this field is automatically populated. If so please suggest the appropriate field in Contracts or in the Customer Master where this information can be held.