How to ration salt in small quantities?
You may need to practice sprinkling salt -- 


Get a large piece of paper or plastic, that's preferably not white.
Sprinkle some salt on it.  Try from different heights.  You might also try different types of salt (I find coarser salts easier to control)
Roll up the paper (or plastic), so you can pour the salt back into a small dish to try again.


Once you're comfortable with sprinkling salt :


Measure out the salt.
Pour the salt into your off hand.
Use your good hand to take pinches of the salt &amp; sprinkle it on the food.


If you're really wedded to a shaker -- you might consider a grinder and coarser salt.  If you know how many grinds it takes to get a teaspoon, you could roughly estimate how much salt is going in by counting grinds.