Loading multiValued fields into Solr via flat file, and possibly value position preservation in those fields
Getting multiValued data into Solr via CSV:

The solr documentation describes a "split" function in UpdateCSV. Essentially, it parses a field value using a second CSV parser. See Solr - UpdateCSV - split. The parameters look like so (adjust field name, separator, and encapsulator as necessary):

f.fieldA.split=true&amp;f.fieldA.separator=%2C&amp;f.fieldA.encapsulator='


Getting multiValued data from separate fields to maintain position:

Since asking this question, I've done some reading about dimensional models. It seems that what I was trying to do is poor design, because it places too many expectations on the application, to much complexity in the warehouse, or both.

When trying to preserve the relationships between two field values on a single record, it's better to store them separately as well as together. Here's a comparison of my former input to the new input:

Former CSV input:

name|licenseState|licenseType
Josh|MA,CA|123,456
Fred|MD,OH|789,123


Transformed CSV input:

name|licenseState|licenseType|licenseStateType
Josh|MA,CA|123,456|MA123,CA456
Fred|MD,OH|789,123|MD789,OH123


This way your application can use the licenseState and licenseType dimension values independently, or it can use the licenseStateType dimension values, all without requiring complicated app or warehouse logic.