Send April and Phil away for the day, limo, nice dinner all that. While they are gone, annouce a free concert to everyone in town and online, put a stage on top of the roof, with all the sound equipment needed for a band to play. Have spotlights in place, pyrotechnics and maybe fireworks, do a sound check and have everything ready to go.... then shut it all down and wait for night, keep all house lights off, limo driver shuts lights off in driveway (fuse problems!).
When they get home at night and go to bed, let everyone into the yard, flip on the lights and sound, blast the music, fireworks and pyro's. As the sound vibrates through the whole house and things are crashing all around with the blinding bright lights, the half awake reaction should be priceless!