This will not work, for two reasons.
First, It will make your paint bleed
everywhere overnight. If you fill your wet palette with water, do a little blob of paint, dilute it with flow enhancer, and leave it for the night, you'll come back to it taking up 3x the space on the wet palette. If you have all flow enhancer instead of water, your paint will spread across the whole wet palette
The reason is... this is the job of flow enhancers.. to take away the surface tension of your paint (which is what makes them stay together as a blob) so that they flow better
Second -- the ratio of water to additive in a flow enhancer is very important, as the additive severely reduces the ability of your paint to adhere to surfaces. Unlike mediums, the ratio of water in a flow enhancer is very high (as I mentioned in the other post, 95% for liquitex) -- which means that as the water in your flow enhancer evaporates, the flow enhancer becomes more and more concentrated, and that just won't work, because then, none of your paint will stick.
But don't take my word for it; give it a shot... it's not like flow enhancer is expensive