I work with glazes that flow in different ways when I do pottery and the interactive chemistry influences that feature. However, several other factors also have influence that are not controllable such as exact temperature for each piece. So my experience in making thing flow is limited.
As for the chemists here, it is likely that they can give you some ideas, but you would have to do the experimenting.
So here are some ideas from a general point of view
If you are working with oil paints, surfactants will likely have an effect on them
I think that Borax as you mentioned has some of those properties plus more.
I could see you using a surfactant and spinning your canvas to get an effect.
You might look up emulsifiers and combine water with oil using them.
I suggested ed the ferrofluid because it might be able to be made with oil paint and magnetic material. Then you could use the movement of magnets to create a pattern.
I was thinking of how dropping paint onto a canvas surface would look if you soaked the canvas in an non polar solvent.
Now here is the rub
how are you going to cure the painting after the flowing is done, so that it will have some durability to it. I suppose you could take photos of it and use that as the art.
Just some starting thoughts.
But you will have to do some leg work
For instance I mentioned non polar solvents
You will have to WIKI and GOOGLE to figure out which might be best.
Detailed Original Blue Fluid Painting inspired by water
was interesting to me as well as your other fluid pieces