Registering/Receiving Inventory with X++ - AX 2012

We are trying to register some product (Site, Warehouse, Location, Serial Number) for a receiving service in AX 2012.  What is the proper way to do this? 

I have it working if the product doesn't require serial number, I just update the line's Receive Now quantity and PurchFormLetter.update using PurchUpdate::ReceiveNow quantity.

But for things that require a serial number, I have to register that product first, then use the PurchUpdate::Recorded quantity to receive in. 

Basically, I need to perform the function of the InventTransRegister Form in X++ code.  How is this accomplished?

Thanks