Zoom88,
Here is a link to Fiero Specific instructions:
http://members.nccw.net/webe/sts/stsfiero.htm
Unfortunately, I don't know of an easy way to get through the firewall. There are some suggestions at the link that might help.
You don't have to connect the control wires to the turn signal indicators. Instead, you can run the wires all the way to the front of the car (you can extend the wires as long as you want -- speaker wire will be fine) and connect to the front turn signals.
Also, this allows you to run the wires on the outside of the car. You can follow a brake line or something to get you to the front. Just be sure to tuck it nice and high to keep it out of harm's way. Watch for sharp edges and hot items.
Good luck, and if you find a good way, please let us know!
-L
http://members.nccw.net/webe/products - WebElectric Products