Creating assembly builds

I just started researching what's involved in creating AssemblyBuild transactions from WebServices.  My current solution is to use a proxy record that is created with Web Services then a SS script creates that actual assembly transaction.  This was a workaround for the days when AssemblyBuilds weren't support in SuiteTalk.

It doesn't look like you can create an AssemblyBuild transaction from an InitializeRecord which leads me to believe we're on our own to define all the member components.  Can anyone confirm this?  To be clear; It looks like I will need to know all the members items and their quantities for the assembly I want to build.  I would then need to construct the AssemblyBuild and add each of these components.