Just do it correctly and get the proper cable casing ferrules from your LBS, You cannot compromise with the brake system and end up having no brakes at the worst moment just because you might not have put in the needed ferrules to properly anchor the housing ends to the frame. You most likely need a hat shaped ferrule that steps down to a smaller diameter so it centers and anchors itself to the flat stops. They come in different sizes and LBS should be able to steer you to the right ferrules if you bring your bike over to them for a look/see.
Good luck with the Puegeot build-up! Hope you get it on the road soon.......safely...
Chombi
84 Peugeot PSV
85 Vitus Plus Carbone 7