Back in the day before 4dF style dice were easily available, there were so many cockamamie procedures to emulate them with normal dice. Fudge RPG included tables for converting to 3d6 or 1d100, and also a weird method of: “This method requires 2d6 of one color (or size) and 2d6 of another color or size. First declare which two dice are the positive dice, and which two the negative, then roll all four dice. Do not add the dice in this system. Instead, remove from the table all but the lowest die (or dice, if more than one has the same lowest number showing).”
Fate asks you to use 1,2: -, 3,4: 0, 5,6:+ which is a method Fudge mentions but dismisses. Starblazer and Anglerre had a 1d6-1d6 method (kinda like Feng Shui) that was also bizarre.
Instead, why not just roll 2d6 normally, like Traveller or Apocalypse World? For unopposed rolls, add 7 to the difficulty, but many rolls in Fate are opposed, in which case you don’t need to do anything. This has the exact same probs as the bizarre Starblazer method and close enough probs to 4dF, for gaming.
For digital, instead use 4d3 if your platform doesn’t have 4dF, and add 8 to the difficulty on unopposed rolls.
Of course, if you do have 4dF, that’s my fave. I love not having to do any math (just remove anything that cancels out, and count up). The 2d6 method is just for when you don’t. It’s the simplest and most straight-forward method.