For a while, Dilbert.com offered a "mashup" function. You took one comic strip and replaced the text on the third panel with your own text. I did some of these, for the greater glory of Tolkien.
February 05, 2011: Topper is wise!
February 09, 2011: The boss regrets his laziness!
February 10, 2011: J.R.R. Tolkien tops the list!
April 20, 2012: The boss is wise!
April 21, 2012: Dilbert meets a giant maggot!
April 27, 2012: Blessed Coffee makes evolution happen!
May 10, 2012: How the wise boss spends his lunch break!
May 24, 2012: Dilbert saves Topper from certain doom!
Copyright note: Dilbert.com permits "posting and displaying a copy of Collaborative Content on a personal web site or on a third party web site" as long as nothing is charged for access. There was an embedding function too, but it was always broken.