When to add salts to RO brewing water

Possible Duplicate:
How can I put minerals back into distilled or reverse osmosis water?

This weekend I'll be brewing a recipe from Mitch Steele's 'IPA' book. The recipe has a very exact water profile, so I decided to use RO water and build the water with salts.

The question is, when do I add these salts? I can add them to the mash water. I can add them to the sparge water. I can add them to the boil kettle. I can add them to all three. What's the best approach?