GPO4 and tremolos

I'm a little dissappointed because there doesn't seem to be a way to produce a tremolo in Garritan's Personal Orchestra solo strings, with or without custom rules.
I've noticed that when using section strings, during playback, the Aria player switches to tremolo, 1/2 half or whole step trills when needed, thus using the corresponding samples.
But when using solo strings, the player doesn't switch to tremolo or trill: trills are played note by note, and temolos are simply ignored.
Is there a way to produce a tremolo? Who tells an instrument if a trill must be played note by note or by switching and playing a continuous sample?
I've noticed that when using section strings, during playback, the Aria player switches to tremolo, 1/2 half or whole step trills when needed, thus using the corresponding samples.
But when using solo strings, the player doesn't switch to tremolo or trill: trills are played note by note, and temolos are simply ignored.
Is there a way to produce a tremolo? Who tells an instrument if a trill must be played note by note or by switching and playing a continuous sample?