An alternative to buying some thicker o-rings would be to unscrew the atomiser slightly. This is a very simple way of adjusting the button throw just so you know....
I tried this but it didn't seem to work right, the atomisers became unstable and wobbly. I have a found a solution anyway and this seems to me to work better for the 510 adapter.
You can see here, I just put the O-Ring (doubled over on itself) over the 510 adapter thread.
As you can see, the brass adapter sticks out at the top now but it works without visible o-rings now, gives me a full button press and actually works out easier for me to clean also.
You can also replace the screw used to a smaller one quite easily also, so for anyone like myself who plans to use AW 14670 batteries, this may be the way to go without having to purchase additional o-rings.
I will still be going shopping though, I am going to try to look for a washer to go between the top nut and the sleeve (where the o-ring previously was located) to add a little bit of a grip for my thumb when using (pushing down on to my little finger). Wish me luck!