There are a whole bunch of pillow covers (har har) on YouTube. Many are in response to their latest promotion/competition, described on their English website as:
Celebrating “the pillows 20th Anniversary Year” titled ‘LATE BLOOMER SERIES’ and the live at Budoukan, we will be holding the Copy Band Event to be aimed at the pillows’ fans in all over the world!!
Basically, they posted a video to YouTube letting people know that the best covers posted as a response will be featured at an upcoming live concert to which the cover group will also win tickets (and some travels costs).
They are known internationally (mostly due to their music being featured on FLCL), so I wonder if there will be many entries from outside of Japan.