internal halyards

The top of the mast is completely sealed except for 6 holes for halyards and a bigger hole for antenna cable. The halyards have to go through the holes in order to line up with the sheaves. The sheaves can be removed which would make threading a messenger easier.
I know copper wire wouldn't work since it would tend to retain the radius that is required to enter the hole at the mast head. Entering from the bottom and threading a wire through that hole at the top would be impossible. Oh, yes, the mast head is not removable. It appears to be welded onto the mast then the weld is ground smooth and painted over. I can detect no seam between the mast head the mast.

Ambianceack, it helps to know others have succeed using the fish tape. The mast here is 35 foot but the halyards pop out about around the 27 foot mark. So, tomorrow its off to the big box home improvement stores to procure a 50 foot tape. When I installed the two halyards I did leave the messenger but that doesn't help since each halyard has its own hole to go through as it enters the mast head.

I'll see if I can snap a picture of the top of the mast showing the holes.

SUCCESS! The electrician fish tape did it. I did have to remove the sheaves. And I was wrong about each halyard having its own hole. There is a slot that the head sail halyards go through as well as a slot for the mains. All in all it wasn't that bad. I do want to thank everyone who commented. If the fish tape didn't work I was going for the vacuum approach followed by the magnet.