You could use zip ties to secure the brake cable or, alternatively, buy yourself one of those trendy toptube pads and thread the cable through that.
(Whilst my use of the word 'trendy' is mildly sarcastic, this is a serious suggestion and - despite the bike snob community's dislike for them - I actually think TT pads are a pretty useful piece of kit, especially if you have to shoulder your bike up some stairs or lock it up often.)
You could use zip ties to secure the brake cable or, alternatively, buy yourself one of those trendy toptube pads and thread the cable through that.
(Whilst my use of the word 'trendy' is mildly sarcastic, this is a serious suggestion and - despite the bike snob community's dislike for them - I actually think TT pads are a pretty useful piece of kit, especially if you have to shoulder your bike up some stairs or lock it up often.)