Citation: Nabokov, Vladimir. _The Annotated Lolita_. 1955. Ed. Alfred Appel, Jr. New York, Vintage, 1991. 20.
The OED has no love for Nabokov. They list "tiddle" as a verb but not as a noun.
When I first read the word, I thought it referred to tiddlywink, but when I finally got around to looking it up on my third trip through _Lolita_, I realized it was probably directly related to two definitions of the verb tiddle:
1) To fondle or indulge to excess; to pet, pamper; to tend carefully, nurse, cherish.
2) To make water, to urinate.
A cupful of piss, a cupful of molestation. That sounds exactly like Humbert Humbert to me.