Disable Forward Button On Playbar

I would like to disable the forward button on the play bar until a specific audio clip finishes playing.  Is there a way to disable only the forward button on entering a side, and then turn it back on at a specific time?  I realize that I can do this by disabling the play bar altogether and creating custom buttons, but I would like to be able to do it on the bar itself.  Is the possible?

Thanks,

Jeff