You can set particles' timescale to 0. All particles which are already on the screen will freeze.
Of course, if you need to control individual particles, you have no other option but to use small sprites instead. Add Fade and Bullet behaviors to the sprite and you should be able to replicate almost all visual effects of the Particle plugin. Plus you can use animations, change frames, rotate and do many other things with events.
If you need physics just for the gravity/bouncing off walls, you can do the same with Bullet, it should be better in terms of performance.