Heres what I said to Fade, so if you are using fl studio you should be able to follow this more easily..
Right you need to use fruity delay 3, two of them. One for the left slap back and one for the right.
On the snare fx inserts add them there.
Switch off tempo sync on both of them pan one hard right and one hard left, i think it goes to the opposite of what you set in ping pong whiich you need to use, you need to use milliseconds.
The left one should be close to 32 ms, a little under and the right one should be a little over, the higher the ms the later the slap back, you dont want it too late though, tune to taste. You have to be careful for phasing, tune until its not phasing, its really obvious at lower ms settings.
The left one set to have bandpass feedback and set the level to around 3.5% and set the cutoff to around 3100hz, the right one the same but have a higher cutoff freq say 5000hz for arguments sake, but Im sure those numbers change depending on the snare being used.
Once they are done it will sound too much, so then just in the snare fx insert panel, turn them down until it sounds just right. Thats what Ive done and I love the result.