Green’s Dictionary of Slang

one who uses a variety of irregular means to accomplish a purpose.

1919		Aussie (France) XIII Apr. 15/2: ‘I’ve just had a long chat with the dear old Colonel – precious old egg! [...] Gave me ten days’ leave to Paris!’ / ‘What again? You priceless old wangler?’ / ‘Yes, again, old bean!’.
1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier 176: Wangler. — One who habitually obtained privileges which he had not earned.
1937		I. Cameron Murder in the Legion 230: ‘[Y]ou don’t know Donald [...] He’s the greatest wangler I know. I believe he could get the Crown Jewels for you if you mentioned you wanted them really badly.