New liquid Miracle Gro bottles

Ok, I know that they 'say' those nifty little bottles can't be re-used, but we ALL know better than that, right? So...what would be a good substitute? A liquid fertilizer concentrate of course, but does anyone have a 'recipe'?
I just used the new dispenser with the liquid fertilizer today and I love it! It's very well balanced and doesn't get heavy after awhile like the big jar did, and no more 'guessing' when the plant food is used up. It's also really easy to switch to just water instead of having to constantly remove the jar and hope you didn't spill the contents, and there was always the issue of where to sit the open jar in the middle of the bed while you simply watered a plant. This is a fantastic improvement.....I just don't want to constantly be buying more refills if there's a more economical alternative.
~Bren