If you want to train grip, find/make a thick bar. I converted one barbell of mine to a thick bar using schedule 40 PVC. Cheap and effective, and SLICK! Which is good as it forces you to really squeeze the bar. An even easier solution would be to buy a small piece of PVC 2" will be perfect, run a loop of rope/chain through it and hang weights from it. Bam, ghetto grip trainer! Load it up and see how much you can pull. Thick bar work translates VERY well to smaller diameter bars.

Pinch gripping is easy too. You can simply pinch plates together (worthless if plates are rubberized as they will stick and kinda defeat the purpose). Alternatively you can make a thicker block by nailing some small pices of 2x4 together and screing a hook in the bottom by which you can suspend weights.

I doubt there is any way to make a ghetto grip trainer. However, Ivanko makes a very nice spring loaded variable resistance grip trainer that is slightly more than one Captains of Crush gripper, and will give you everything from "grandma's fart will close this thing" to "might break the Hulk's knuckles" and all inbetween in fairly manageable steps.