From what I've seen, the reason that you sometimes don't have enough minerals to queue up a second worker is because of the far mineral patches on each map. The workers at farther away mineral patches (ones that require 3 workers for "perfect" saturation) provide less minerals over a period of time then workers harvesting from the closer patches, and when you are making your second this translates to having 45 or 40 minerals when you need 50 , because you have to wait for the workers harvesting at the 2 (at least on steppes of war, where I tested this) far patches to arrive. Depending on how you split and on where the game engine put your workers initially, there will either be 1 or 2 workers harvesting from a far patch, resulting in only having 45 or 40 minerals respectively.
The thing that I've been doing to fix this is to perform a normal split, wait for any workers that went to a far patch to finish their first round of 5 minerals, and then manually move them to an empty closer patch. It's a bit tricky to do correctly, but every time that I've managed to do this I've been able to queue up my second worker.
On this note, I've also been trying to avoid utilizing my far patches for as long as possible. I've been trying to make a double worker chain on both close patches before sending my first worker to a far patch, and it's been remarkably succesful- I've been able to increase my build order timing by 3-5 seconds doing this.
It's better then just spam clicking in the early game anyway.
Edit: I guess the name of the thread is a bit misleading, this doesn't change the way you split but what you do in the first few seconds after you split.