I've started playing with nlapiTransformRecord to create invoices from sales orders. 

I want this to work for my sales orders that have billing schedules and to only raise the next invoice based on the billing schedule.

My initial tests have raised the balance of the sales order on the invoice.

Should I be looking at parameters of the nlapiTransformRecord method?
Or am I effectively going to need to interrogate the schedule and the invoice history mix in a bunch of logic and raise the next part invoice myself?

Anybody tried this before?  I'll consider web services over Suite script if there is better support.