So I finally have something I feel works for our needs. I ended up ditching all the “slick tricks” and just did a customization featuring an Ultragrid with a couple buttons. I modified Extended Properties to prevent directly editing the columns I am auto-populating.
The stock behavior of the Child UD Wizard had a few odd behaviors.It would delete all rows if you did not select any. I think this is because it’s relying on you to hit the Delete button to delete a row… but I added that method to the Delete button I created. So I was able to fix that.
It also would insert a row but not call the method of the GetNewUD13Record() when you hit Enter in the grid - which left a partially filled row that would never save. So I added a Cancel to the beforeRowInsert event and then called the GetNewUD13Record() method. Now when you hit Enter, it acts just like you would expect.
Thank you everyone who has commented and helped. I’ll have to figure out which is the closest to the solution 
