Personally, with bar end shifters I saw a few cm (3cm?) off the end of the bars to avoid the bar / lever combination being too long and risking contact with knees. Then I have the cables exiting the tape about 2cm from the levers, with a sculpted bit of high density foam to guide them downwards to make space for fingers on the drops. By having the cables so exposed, changing the outers requires minimal faffing with the tape, and the curve of the cables is very smooth.