Green’s Dictionary of Slang

used to denominate a person or object the name of which one has temporarily forgotten.

1999		T. Mo Renegade 50: They can cut my legs off and I kneecap your man Atty Whojamaflip in da head.
2000		Guardian 16 Feb. 18: That Malcolm Whodyamaflick came round.
2003		McGill Reed Dict. of N.Z. Sl. 230: whojamaflung/whojamafiffle Thingummyjig.