At one time, Jun Planning was going to release a new eye mechanism that would allow you to 'sleep eye' the doll--in effect to be able to hold the eyelids down without putting tape over the buttons at the back. They couldn't figure it out, the doll that was supposed to have it was delayed, etc. That was over a year ago.
Here's an easy fix that will let you modify your current dolls to have sleep eyes in about 15 minutes.
You will need:
Craft blade like an exacto knife
Phillips head screwdriver
The first thing you need to do is depress each of the eye buttons and make a pencil line indicating where the natural stop is. Do it on the bottom as the top buttons go in too deeply.
Open up the head and remove the back plate and the eyelid levers. holding the button on the outside to line up the marking you already made, made a pencil mark on the inside. This gives you a guideline of where you need to cut.
Now get cutting.
You only need to cut shallow notches, about 1/3 of the way through the thickness of the post. Just enough to get a good catch on the hole they poke through.
Put the levers back in, and screw the head back on. This is how the blink buttons should look.
Give 'em a press. They should catch naturally since most people press downward as they push inward. Sleep eyes! Now to release them, just push the buttons upward slightly and they'll spring right back out.
So long as you make your measurements properly, and remember basic sharp-things safety, you shouldn't have a problem. Enjoy your newly sleep-eyed dolls!