You don't need to use the zip-ties.
Your local bike shop should have cable guide adapters that take a hydraulic hose and will fit inside your cable stops.
I can't remember their proper name, but I always get mine from Leisure lakes bike shop, and they come in polished Silver, dull Silver or Black, and are made by I.D.
Another option used on mine...
http://www.retrobike.co.uk/forum/viewtopic.php?t=10621
...is to use a wire between the bosses with a sleeve that takes the Magura hose inside. Again, I got this from LL and it has been used since about 2000 (on another frame). If you look hard enough, it is just visible on the top tube. I think I used this method because I had a problem with the cable adapters on this particular frames' cable guides.
