Planting - use tweezers for individual stems (best, if you have the patience of a Zen master or the speed of a sweat-shop seamstress) or a few stems at a time. Poke 'em down about 1.5x as deep as you want them, then gently grab the exposed part and pull it back out 1/3 of the way. If it's a long one, you can trim it off and repeat with the remaining top.
Plant them only in unshaded areas. If they still refuse to stay down, you will have to trim frequently and/or add more light.