Given that's a dynamic animation, how would you want it to work? Keep swirling as the brush is moving? For a fixed time afterwards? Use the spacebar to continue animating as with watercolor?
I'm glad you asked.
In the sample provided you can freeze the fluid simulation.
Additionally Imagine if you would:
The best program I've tried for fluid dynamics is Rebelle 4, free trial available.
Try app called Verve painter