Hi guys!
I could really need some help.
I own a Trek team time trial bike and have trouble with the inner cable routing for the rear derailleur.
Because of some problems with shifting I had to pull out the cable in its entirety and now it’s nearly (I hope) impossible to get it back in there again. It’s one thing to push it into one of the holes, but quite a different story to lure it out on the other side.
Any ideas how to address my problem? Of course I can have it externally on the frame, but I would really like to use the internal cable routing.
Any tips are welcome.
Have you tried a large magnet on the outside of the frame? You need to use a stainless steel cable for the best results.
Good luck! if you take it to a shop - take a 12 pack with you 
I’m not intimately familiar with THAT bike, but I’ve always used some string, fiber tape etc, inset it in the exit hole in a loop, push it all the way to the other side of the frame cavity, then “lasso” the cable head. You can actually push the cable well down in the frame, past the string lasso, then pull the cable against the opening, this way youll know for sure you can catch the cable head as you pull it back up, then sort of “fish” the cable out.
I hope this is applicable to that frame, its worked for me with other internal cable routing issues.
One note, use something with some rigidity as the lasso, i.e. stiff twine, thin wire, so you can control its insertion better.
There are a million “wrong” thoughts related to the above description if taken out of context…
Thanks for your advice, although I found another solution to the problem.
I thought I might share it, in case someone else happens to run into the same problem.
What I did was (I hope I use the right words) I removed the headset and the head tube entirely so I could work with the cable from inside that space. Then it was pretty simple to push it upwards and through the right hole. 
That’s just one of the problems associated with inner cable routing, another is that it is really difficult to do a regular visual check on the cable condition.
Which is why I always buy bikes with external routing.
String and a vacuum cleaner.