Dialing Contribution Aggregate by Relationship back a few year
Answering my own question: 

My fix was to edit a file in "all", which isn't ideal since it'll get overwritten when updating CiviCRM, but I can always re-apply it.

Edit file: sites/all/modules/civicrm/CRM/Report/Form/Contribute/History.php

Change Line 61 from $yearsInPast = 4; to $yearsInPast = 20;