Hi richard.joseph.pollak,
I don't know of a way to do that in iparts.
What we typically do is to right click on the column (Length for your example) and choose Key, and then choose the Key number. Then close the iPart author table, and right click on the table in the browser and choose List By Keys.
This assists with placement, but doesn't really do much to help you fill out the ipart table. If that's what you're after, then you might edit the table in Excel.
Does that get you closer to what you're after?
Edit: just for clarification. Multivalue Parameters were created for, and are used with iLogic. iParts simply do not know about Multivalue Parameters.
I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com