When I joined the book club I had more or less already decided that I would not go for transcription - unless motivation and opportunity strike at some point. I’d like to share what I think are the benefits of this approach, for those who still haven’t decided for themselves. (TL;DR the bold lines should provide the gist of what I have to say.)
Mangas are not novels
I’ve read mangas before (Bleach, Dragonball and Naruto tbh), so I know that most of the text is dialog. I don’t have to put up with “The hero does X while Y. The scenery A profits especially from feature 12 as exhibited by paraphernalia 40.” Context and vocabulary is mostly narrowed down to the actual action and character development, I suppose, and culminations of dense text are an exception. (I remember especially a little slice of life from the artist himself between Naruto chapters.)
Reading or “pretending to speak Japanese while really just mimicking the mouth-noises as indicated by the script”.
Like when I looked into that free Yatsuba! section the other day. I mouthed/pronounced everything, understood what I did, and filled the gaps with deduction from the context. When curiosity really got me I used a translator and thus got around a little new grammar and vocabulary here and there, piece by piece.
I wasn’t sure if this is cheating inside the book club, but meanwhile I believe it’s even appreciated. Thanks to @ChristopherFritz I feel encourage to stick to this intent, enhanced with what the book club provides and perhaps my own occasional question on top.
Put it down; read it again; repeat
Another key to this concept is that I don’t intent to go through each chapter only once. As with Yatsuba!, I’ll look at a few pages at a time, get the idea from the pictures. Return to page one, read and pronounce, maybe look something up. And repeat, maybe not on the same day, but each week I will probably again and again return to the first page and read it again. Eventually memory and pattern recognition will come, effectively supported by having probably memorized every word in the plot at some point.
Finally: No preparation required
You can just pick up the book when you got the time and enjoy speaking some Japanese for a couple of minutes, even if you don’t understand it yourself. This should feel more like a brief but crisp jog in the afternoon, not a full-blown session at the fitness studio.
In a nutshell I believe the mere act of “pronouncing” the sentences by way of reading the hiragana and furigana, while following the plot provided by pictures, will already nurture the synapses that @ChristopherFritz refers to as pattern recognition. It needs real focus and the will to understand the foreign language, but then it will teach you something even if you didn’t mentally/manually transcribe every single word and particle.