French equivalent of "I just wanted to say a quick thank you for ..."

Question

I wonder if there is a French equivalent of this English expression. I mean, without using the usual suspects: « merci d’avoir fait ... » or « je te suis reconnaissant d’avoir fait ... ». Something suitably casual, something you say in passing, when you don't want to make a big deal out of it.

Answer 1

For the “quick” part, I’d rely on the notion of “small,” to which you could add either “vite fait” or “en passant,” (or neither, and maybe even both):

“Un petit merci vite fait”. (from LWS.fr)

“Un petit merci, en passant” (from blogues.lapresse.ca)

As to how to present/preface the sentiment, you could use:

“Juste un petit merci … pour” (from jeuxvideo.fr);

“Voilà un petit merci … pour” (from jeuxvideo.com [down in the comment]);
or (unless you find it too close to the usual suspects)

“Je voulais juste te dire un petit merci … pour” (from cuk.ch)

Answer 2

Je ne trouve rien de plus. Je peux très bien imaginer un dialogue qui contiendrait:

Ah! Au fait... merci de m'avoir dépanné ce matin, j'étais vraiment coincé.