If you manage to flag the lines concerning the first invoice and seconde invoice on your SO (for example, by adding a checkbox '2nd Invoice' on the Sales Orders and Revenue Arrangements which you will then map in the revenue recognition fields, with source field = 2nd Invoice / target field = 2nd Invoice), then you can use the scripting logic that I've created. This involves running a MRS on the Revenue Arrangements (RA), and if the '2nd Invoice' checkbox is checked on the Revenue Elements line, then the 'CREATE REVENUE PLANS ON' value changes (from fulfillment to billing). This way, you can generate your revenue recognition at the time of fulfillment for your items from the first invoice, and generate your revenue recognition at the time of billing for your items from the second invoice.