As the OP has implied
, if the angle is less than 45° (indeed, even if it is 45°), there is a problem IF one wants to comply with the recommended minimum bending radius for SWA - and, as the OP's maths has correctly concluded, a 45° hole through a 300mm wall would be about 420 mm long. I know what I would probably do, but I'm not going to 'recommend or advise' it
An excellent idea but, other than for people a lot more clever/skilful than me (and particularly when one is not drilling exactly horizontally), that presents a next-to-impossible 'aiming problem'
Kind Regards, John