Some frames are difficult. My old Orbea has molded in cable stops, with a tiny hole in the center, just a little larger than the wire cable itself. This would never work with gravity, or a vacuum cleaner & thread.

The best way is to push some temporary thin tubing onto the existing wire from the back end. It makes a guide through the frame. Push the new cable through the tubing, then pull the tubing out the back.

See my summary post here.
And more details here.
The tubing: