I have a bit of the shimano full-length gear cable sitting about and am thinking of sticking it on a bike with normal cable stops.

I’ve got a neat-ish idea for using wee zip-ties on the cable stops, but would like to do something decent with the BB cable guide.

Can I buy something that screws in there that’ll hold it all in place? My pathetic google attempts have led me nowhere.

P-clips are what you’ll be looking for. Maplins have bags of 100 for a couple of quid, or try an electrical supplier(get your zipties there too, usually much cheaper than the high street).