Not quite the same, but you can simulate the effect by taking off the PS belt.
As for a true mod, assuming it's the same system as for the 944's (I can't imagine why it wouldn't be), you'll be looking at greater lock-to-lock. I got this info from the 944 world:
manual
----------
steering wheel ratio 22.39:1
turns lock to lock 3.84-4.02
power
-----------
steering wheel ratio LHD 18.85:1/RHD 18.96:1
turns lock to lock LHD 3.24/RHD 3.26
IMO, it's not a worthwhile modification for a street car, unless your PS system is completely toast.