Actually, you can fake it with runtime expressions on the spriteScaleXPP and spriteTwistPP attributes. It IS a fake, but depending on what you're going for, it can work.

Try something like this.

Creation expressions:
particleShape1.spriteScaleXPP = rand(-1,1);
particleShape1.spriteScaleYPP = rand(-1,1);
particleShape1.spriteTwistPP = rand(-180,180);

Runtime expressions:
if (particleShape1.spriteScaleXPP > 1)
{
particleShape1.spriteScaleXPP = -1;
}
if (particleShape1.spriteTwistPP > 180)
{
particleShape1.spriteTwistPP = -180;
}

particleShape1.spriteScaleXPP += 0.01;
particleShape1.spriteTwistPP += 2;

Attached is a sample file to see what I mean.

I'm very excited to help Mike after all the times he's helped me. I hope it works.