The e-gate is by far the best part of emirates gold. although I have heard that anyone can simply pay a small fee and get egate access.
Anyway, the office they tell you to use is actually after customs. However, I got my card activated just before passport control at a very inconspicuous but convenient location.

When you get to the top of the last escalators just before passport control, turn to your left. At the very end of the line of counters, is a desk with a guy (no sign, nothing.) He has a camera and tripod for taking a picture (of your passport picture - bring one - and bring the gold card). I then had to get my passport stamped by another guy in a little room. The whole thing took 10 minutes.

The guy stamping my passport actually constituted passing through immigration, so if you are immediatley connecting onward make sure that you proceed on through customs and then exit the country officially again. I did not when I did it and had a real hitch when I tried to enter the next time (It was as if I was supposed to already be in the UAE).

The card is great. never a hitch since.