The ratios, ppm's. stay the same regardless of volume. I guess if you just want x milligrams in the kettle you could just add it to the kettle.
Saw this when you posted but didn't have time to follow up. I didn't track with your answer though. Isn't the ration, i.e., the ppm, going to change based on how much water is ultamately added to the mash and sparge? Fior example, using the EZ calculator, you estimate total gallons for mashing, and total gallons for sparging. With whatever salts you've added, and I add all of mine into the mash, you get a theoretical ppm based on the total water volume. The mash water volume is easily measured. But let's say my sparge water volume is estimated to be 5 gallons. However, I wind up adding a total of 10 gallons into the mash tun. Are not the resulting ppms lower (diluted)? Maybe I'm not looking at this right.
Cheers!
PS For even more love, look for my newest thread "Where's my bitterness?!"