Aloha eleanorg!
Depending on the sizing, I do a combination of the following:
1) Fill the hole with appropriate sized seed or bugle bead(s) so the stringing material or head/eye pin fits snugly through.
2) Use curved shaped beads http://www.landofodds.com/store/angelwings.htm or buri beads come in this shape also, on the string/pin that will be hidden behind the button face. Use similar colors to the button, so they are camoflaged a bit. This props up the button and keeps it facing up at the correct angle.
3) Depending on the design and weight balance, once you've strung everything in place, you may need to use a touch of Hypo Cement inside the shank hole to keep the button from spinning around.
Hope this helps! ~alohabc [8D]