i spent a while pondering this one, in the end I just junked the standard coolant/breather pipe assembly as trying to separate the 2 pipes was gonna be a pain in the arse.
The real J's kit is supplied with a replacement breather pipe which looks like the clear/braided hose in the attached photo.
I just used a piece of fuel hose i had lying around (pretty much identical to the stuff in the photo) to reconnect the coolant line with a couple of jubilee clips on each end to keep a tight seal. The diameter needed for the breather pipe is slightly larger in diameter than that needed for the coolant pipe though.
Works a dream, plus looks pretty good to boot!!