You'd have to export the appropriate Genesis figure to ZBrush first, then modify/model it there, and then bring it back to Daz to retain the topology and save everything as a morph.
Although I guess this is a bit advanced, but there are plenty of guides on youtube. 🙂
Just kidding, as Legolas said, you would have to alter the structure of the hand. IF you are new to 3D I would not recommend it.
I did a quick search, there is a character for Genesis 3 Male,
Varginha Alien for Genesis 3 male
can be found at renderocity.