My fiero had this exact problem just before i put it away last winter.
all of a sudden it was hard to get into gear, then one day it stopped all together.
I'd push the clutch in and the slave rod would move only a bit, not enough to move the throwout arm.
I read all the suggestions posted on here from our wise community and went through every possible cause.
You might want to check these out too.
Bent clutch pedal - The stock aluminum pedal can bend over time causing shifing problems.
Upside-down Banjo - according to V8Archie, some 87-88 Fiero's were assembled with the banjo upside-down (this part is the connection between the pedal and the master cyl)
Leak - You might have an invisible leak. Pull back the carpet & look.
Check out
http://www.v8archie.com and click on "archisms" on the left side of the page. He has some great tips on clutch issues there.
In the end, after i had checked everything twice and bled the clutch for 2 days with my dad with no positive results, I decided to put a band-aid solution in place.
I didnt have the resources to make a longer rod for the slave so I just got a 1/4" thick steel washer and put it between the rod and the piston in the slave making the rod come out just a bit longer so it could push the thorwout arm all the way (Similar to your vise grip method, )...now it shifts even better then before...for now at least!
Of course band-aids are meant to come off at some point...so I should look into a new slave soon.
Maybe you got the wrong slave?
[This message has been edited by Dougie Murder (edited 05-01-2010).]