K100RT/LT top brake hose is around 2" longer, could fit one of those (then it's not a 'custom' part...) or just get a different longer hose.
Other than that, I don't know of a way to make a hose longer without making a longer hose.
Of course, you could move the grips/controls further in along the bars (might need different bars) which would make it narrower but give a little more play in the hose.
Or have I misunderstood?