Drill a hole. Then twist the drill around to enlarge it in the direction the line will travel. Done.
The F18 rules requires spin poles to have a "blunt and rounded" tip, and that's for a good reason. IHMO all classes should do the same: Without one those poles are awesome cookie cutter and can cut through anything. So please make sure you plug the end of you new spin pole properly.
As usual Pepin is right on. After drilling, angle the drill in the directing the line will run to fair in the hole edges. Then I'd add the additional step of taking a bit of rod/screwdriver shaft at nearly the same diameter...leverage th rod in the hole so it bends the alu outward at the forward side and inward at the aft side. Then use a round file to put final deburring on all the edges.
This basically makes a very clean through-deck. I've seen this done on many keelboat masts & extrusions.
