Welp, this is odd, the episode is actually on July 12, NOT May 1st!
In the special, Patrick Star (Bill Fagerbakke) takes the characters to the surface world to distract them while birthday party plans are being made in Bikini Bottom. There, the voice actors portray slightly different versions of their characters, not with sponge or starfish costumes, but by wearing clothing and acting as human versions of their underwater doppelgangers.
They end up at a restaurant called the Trusty Slab, which sounds much like their watery hangout, the Krusty Krab. A brief clip showed Tom Kenny flipping burgers at a frenetic pace, much like his character, SpongeBob.