The OEM piece is attached with clips - one side clips onto the lip and the other side at 90° clips onto the metal edge of the weather strip.
At one time there was someone selling a home made version that attached to the lid and the other side attached to the firewall - this prevented the issue of water still falling onto the manifold as it would still happen with the OEM one when you opened the decklid. This was several years ago and doubt that they are still available or who it was that had them for sale (might have been one of the southern US Fiero clubs for that matter).
edit: try searching for recall weather strip
link for the aftermarket ones: //www.fiero.nl/forum/Forum2/HTML/123091.html
picture of the aftermarket one: //www.fiero.nl/forum/A...040710-1-036753.html
link that has a picture of it mounted showing the clips: //www.fiero.nl/forum/A...040710-2-046528.html
[This message has been edited by Mickey_Moose (edited 06-28-2013).]