take a thread, as in a skinny bit of fabric, the stuff you sew with. pull off enough to fit through frame from hole to hole.
take a vacuum cleaner, the thing you drag round the house once a week in an attempt to make it look something liveable and not a barn.
Tie thread to handle bar (or other fixed bit of bike near entry hole) then place other end of thread near one hole or threaded just slightly in to hole.
place vaccum cleaner at other hole and turn on.
thread will now perform magic trick and try to break vacuum cleaner by leaping through frame from one hole to other.
untie (or snip) thread from handle bar (or other fixed bit of bike you tied it too), tie it to the cable, I like prusik with a a double overhand hitch. I tend to back this up with a bit of elechicken tape for safe measure.
pull cable through frame. if frame is complex, use a long length of plastic after the thread before you try the cable. You'll get a better connection to the cable. I stripped a plastic bottle in to 2mm wide filament a few years back that works perfectly.
take ******* annoying magnetic routing kit and chuck it where it belongs, in the bin, waste of money, time and good magnets. you will never see a shop use one, if you do, it's because the cleaners broke, quite likely because the workshop monkey got his cock caught in the spinny bit, dirty bugger. (note, not every spanner weilder is a monkey, some are apes.
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