Elastic bands and bread ties are the quickest and fastest.
Here's the bread tie, if it's white it hides nicely and bends the way you want it to.
Then there's the rubber band hold, very quick and simple. Hides very nicely in a long sleeved costume but shows against the white gloves.
I definitely think you can do more with this cute little elf by separating the hands. As I have done in this picture, you can pin their arms and legs in a climbing effect and dress them in any costume.
This is way to much fun! I'd love to hear some other idea's out there.