Why not just get Mr Oswald himself to go up to the sixth floor and pretend to shoot at JFK?
That would be very dangerous, Lee knew that the Secret service would probably kill him ( Actually the conspirators would have loved for Lee to have agreed to be at the window.) After the Walker incident Marina had told him that some other party could have shot Walker and it would appear that Lee had been the shooter, so Lee wouldn't have been there on the sixth floor. However, I believe there is a very strong possibility that Lee could have been the person who planted the evidence ( Shells, and rifle) BEFORE the event..
---OK Lee, so we're gonna to do a fake assassination attempt to get you into Castro's good graces.
---Sounds good.
---Fake shots.
---Sounds good.
---You up at the sixth-floor window.
---Sounds good.
---Your Carcano.
---Sounds good.
---Shells left by the window.
---Sounds good.
---Lots of folks down below in the crowd to see you up there.
---Sounds good.
---Might even be some photographs taken.
---Sounds good.
---So it's real important there's no doubt in anyone's mind that it was you done it, otherwise Castro will have you killed.
---Sounds good.
---We gotta get this right.
---Sounds good.
---So we're gonna get someone else to be up at that window pretending to be you.
---Huh?
If Lee had been behind the window and had escaped from that site, he would never have left the building , because there were plenty of law officers in the area to have sealed the building immediately.
---Also, seeing as we need to get you out of the building alive and all, we're gonna make sure the guy impersonating you up there doesn't look a whole lot like you.