I've created a spreadsheet that calculates the recipe for creating mixes with the desired NPK ratio and I thought I'd share it with the forum members. It should work with any NPK ratio you wish to mix. Simply input the desired NPK ratio, along with the NPK ratios of the starting mix as well as 2 "adjuster" fertilizers and it should give you the exact mixes. I'm still testing this so perhaps some of the veterans here who mix their own fertilizers could try it to make sure it gives the correct values. I've tested using JoeReal's examples in the FAQ post and it works for all of those. Here is the url for the .xls spreadsheet:

http://www.2shared.com/file/3630056/1feded07/Fertilizer_Conversion.html

Edit:

When I posted this, the file hosting link was not working. Here is the same file using the hosting built into this board:

http://www.uploading.com/files/BCE80PPL/Fertilizer_Conversion.xls.html

I've uploaded the file to a more permanent place in case it is deleted. Here is the url:

http://brad.kairdolf.googlepages.com/FertilizerConversion.xls