toma,

It appears you're not the first with the theory. Found the reference below on the Web (isn't it a splendiferous thing?) on a page devoted to - of all things - the lyrics of The Grateful Dead, on whom, I should add, I am no expert. [And what an abominable sentence that was for only my second post - please be gentle.] The song in question is apparently called the Mississippi Half-Step Uptown Toodleoo. My cousin uses the variation "toodle-pip" allegedly mentioned in the OED, although how "oo" becomes "pip" mystifies me! Anyway back to the URL (hope I get this hot-link thing working first time!):
http://arts.ucsc.edu/gdead/agdl/halfstep.html
and follow the link on the word Toodleoo to:
http://arts.ucsc.edu/gdead/agdl/halfstep.html#toodleloo

For those not inclined to click, it reads:
Toodleloo
From the Oxford English Dictionary:
"toodle-oo int. colloq. [Origin unknown; perh. f. TOOT (An act of tooting...)] Goodbye. Cf. PIP-PIP.
1907 Punch 26 June 465 'Toodle-oo, old sport.' Mr. Punch turned round at the amazing words and gazed at his companion. ...
Also toodle-, tootle-pip.
Partridge speculates:

"...or maybe, as Mr F.W. Thomas has most ingeniously suggested, a Cockney corruption of the French equivalent of '(I'll) see you soon': a tout a l'heure."

For the REALLY interested, the Partridge reference is:
Partridge, Eric. A Dictionary of Slang and Unconventional English : Colloquialisms and Catch-phrases, Solecisms and Catachreses, Nicknames and Vulgarisms. NY: MacMillan, 1984.

Hope that helps!