How in the world should i guide the cable from the hole in probably the downtube, to the hole in the BB?
That parts sucks, whether you do custom drilling or buy one that has been done in the factory. I had to route the cables without guides ones on a Kestrel Airfoil frame. I ended up fishing the cable through with some iron wire bent on the tip to mimic a hook. Make sure to 'fish' through something like a thin shoelace or a textile wire first, as these are more flexible than your shift cables. After you have done that, you can tie the shoelace to your shift cable and pull it through.
Another option is to have the cables exit on the down side of the down tube, just before the weld off the bottom bracket and route the cables externally from that point on. Cervelo uses this method for example.
Or go the Specialized? way: