A great many plants will root from their stems.
All you need to do is cut off a growing part of
the plant, several leaves and adjoining stem
just enough to allow the leaves to stick up
above the water. Strip away lower leaves,
and pinch off blossoms or terminal bud
(the newest pair of leaves) at the growing tip.
Then fill a nice glass vase with pebbles, sand, or even marbles, tuck the cuttings in place, and fill the vase with water.
If you don't know for sure the particular plant will root from cuttings, you may want to start this some time before you want it ready, and be sure to keep the water level constant during that time.
