THis is pretty easy, just one hole to drill, if you remove the unused cable guide at the bottom of the down tube you can fit a 5/16" drill bit through it to drill a hole through the bottom of the seat tube above the BB shell. Using a blue wire hose puller tool it was quite easy to get the hydro line for the dropper post pulled through the frame with it exiting at the top of the down tube through the hole that is there for a front derailleur cable, which is unused as the bike is 1x12.

Here is the angle of the drill when I drilled the hole, The hole is well below the weld so there are no issues with structural integrity.