This article contains two stored procedures that will insert/update data in Extender tables. The code is not fully flushed out for all of the data types, but it supports text and numbers.
If you use it and update it, email your code to support@ and we'll update it here.
EDIT 11/16/2018
In response to customer feedback, new proc below updated to handle dates and dropdown values
EDIT 9/29/2020
Rewritten to include suggested code from the comments below.