Use Body Double® Skin Safe Lifecasting Silicone Rubber fast set
and dole it out with a tongue depressor into paper cups about 1/2 full. It is a two part RTV product, so when you are ready, mix the green and blue thoroughly.
Put a 2 foot square of brown butcher paper down on a table so that you don't mess up the table during this process. Place your hand firmly on the paper, and use a Popsicle stick to apply a "beauty coat", a thin coating to the hand. That will allow you to pick up all of the detail. Once the first coat is on, slather the rest on so that your hand is covered.
Wait about 20 minutes for the "fast set" to set.