Se7eN:
Check with the CFRS or where you are doing the PT Test, confirm if you are doing a grip test.
If you are, simplist thing, scoot down to your nearest living aids store and ask for a squeeze ball. Same idea as the stress ball.
If you are working out, talk to a muscle tech, one of the best things I found (IMHO), is when you are doing curls, let it roll slowly down your hand and then slowly roll it back up. Kind of like opening and closing your fist.
Cheers.