Nigel, Well, thats one way to "avoid" the question, your solution probably works just as you described.
However, i believe that the initial question merits an answer, regardless of other workarounds.
I am grateful for your input, especially when you don´t agree with me, since that´s when i learn the most.
For me personally, its a question of finance versus time.
I have designed and ordered custom PCB´s for this project (will be posting more about it under the same tag) and even tho i had to ditch some of the component pcb´s due to negligence on the design-stage, i find it hard to motivate yet another PCB order.
The issues with the scrapped PCB´s are too numerous to mention but their functions will be replaced with soldered proto-boards.
The battery compartment (where the previously linked auto-off circuit resides) has about 45mm inner diameter(tube, L=35cm), so its a wee bit more spacy than 19.5mm (inner dia, handlebar, usable L=15cm)..
The reason behind not being "able" to go for a bare chip is that i dont think i´ll have the space for a (big enough) chip and its requred hardware inside my handlebar tube, while a arduino nano with the wires soldered directly to the board (no headers) will fit like a glove, with not a mm to spare. (18.9mm with electric tape)
This means that my circuit ends up in the middle of the tube, eliminating the possibility of the circuit shorting against the handlebar tube.
But please enlighten me, what is it about the "real" arduino that takes time compared to the "bare chip" at bootup?
I always figured that the arduino is just a "breakout board" for the ATMEGA processor onboard..