The rans Main Spar is an Ali tube leading edge and I've no wish to attack it, especially near the fuselage.
Yeah, don't cut that in any way, anywhere.
Could a pipe, cunningly curved, be introduced externally to the wing - with an aperture forward facing and its tail end feeding a pitot type hose leading to a cabin reed horn near my head ?
In my opinion, it could work, after a lot of experimentation, and next tries. Having done a lot of flight testing to locate/qualify new static ports on an aircraft, I would not attempt this. I'm not saying it can't be done, just that I would not invest my time in it. For the value of your time you'd get into it, buy an aftermarket AoA system, and devote good effort to setting it up accurately, you'll be happier in the end.
That said, there are some important aspects of setting those up, and I've seen it done wrong. Indeed, I found an error to the unsafe side in one AoA manufacturer's instructions, so there are some things you have to know. But, correctly set up, they're a good system.