Green’s Dictionary of Slang

(Aus.) ‘a catch word satirically applied to a popularity-hunter’ (Downing, Digger Dialects, 1919).

1919		W.H. Downing Digger Dialects 24: freeze-a! — A catch word satirically applied to a popularity-hunter.
1924		(con. WWI) A.G. Pretty Gloss. of Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: freeze -a. A catch word satirically applied to a popularity-hunter. Corruption of ‘For he is a jolly good fellow.’.