Green’s Dictionary of Slang

gee n.2

also G
[gee (up) v. (1)]

1. [late 19C+] (Aus., also gee-er, gee man) one who ‘gees up’ the potential customers into a sideshow, strip-club, confidence trick etc.

2. [190s-30s] idle chatter, empty talk, ‘blarney’.

In phrases

put in the gee (v.)

[1920s+] to deceive, to ‘tell the tale’.

put on the gee (v.)

[1920s+] to boast, to brag, to ‘swank about’.

sling the gee (v.)

[1920s] (UK Und.) to take part in a swindle.