For some people it's DIY. For others, not!
The trick is to get the exit hole on the off side to come out exactly where you desire, exactly.
There is a trick that some have used.
Do all drilling with a drill press.
Drill a small counter sink centered at the exact point(s) on the off side.
Mark your entrance point.
Place a ball bearing on the drill press table exactly centered on the point of the bit. Use vise, etc.
Then set the counter sink hole (bottom side) on that ball bearing.
Hold the entrance make exactly centered on the bit. (This is why some if not most use gunsmiths)
Drill the hole and it will be where you wish.
That's the best I can explain it. I'd practice on some rough lumber until you get comfortable with it.
Once you're comfortable and do the first one you will be as much of an expert as anyone.