Green’s Dictionary of Slang

wimpo n.

[wimp n.1 (1) + -o sfx (1)/-oid]

a weakling, an ineffective person.

[UK]T. Blacker Fixx 306: Our friend [...] being in fact a bit of a wimpo when it comes to an up-front confrontation.
B. Simpson Running with God 87: I was no wimpo California granola-crunching hippie wannabe.