I assume you mean to another player? Its not possible to transfer play money but if you open a new table with the player you wish to transfer to, you can 'raise and fold' some chips to them, or if you have a lot of chips, play a heads up and intentionally lose.
Be advised that this is technically classed as chip dumping and COULD get you thrown off the site, i've never done it and never will, but i'm sure it wouldn't cause too many ripples doing it with play chips.
Interested to see what other people think of this actually...