In the scenario I'm proposing:
Frazier had no reason to suspect Oswald was carrying a rifle to work that day and accepted the curtain rod story.
After the event he realised it was a rifle and that no-one would buy his "But I thought it was curtain rods" excuse.
On reflection, it was obviously a rifle.
Oswald had no need for curtain rods.
He never mentioned curtain rods to anyone else only Frazier.
It was a totally
story.
But Frazier could've only known there was curtain rods in the Paine household because Oswald had told him about them.
And there were two curtain rods.
Only two curtain rods.
And they were both still in the Paine garage after the assassination.
Because Oswald never took any curtain rods with him.
He took a rifle.
And Frazier had to convince everyone that the long package he brought with him that day could not have been a rifle.
Everything else about his story could be exactly as it happened except what the long package looked like.
He had enough time to come up with his story in the missing few hours between him going home after work and Linnie Mae approaching Adamcik outside the Paine house.