The functionality to create different assemblies with one simple command, such as creating a pre-filled pallet is not yet available in Process Modeling.
To get around this you can utilize two feeders, one that creates the pallet and another one that creates the components on the pallet. You can then populate the pallet with Transport Pattern In statement.
I made an example layout that has two feeders and one sink. You can adjust how the pallet is formed by modifying the TransportPatternIn, Product Creator and Transport Link properties.
PM_Pallet_example.vcmx (836.4 KB)
Be sure to disable the accept all product types property for the transport in statements, as you only want to transport in the specific products at a given time.