I think the spice solution also needs to be saturated, or at least as concentrated as possible.

Otherwise the reactants will stay dissolved after part of it crashes out - I think FASA works because we move on the edge of solubility curve.

It will be probably hard to dissolve any fumaric acid in already highly concentrated spice solution - if it will dissolve at all. You really need that little excess of acetone but then it will be even harder not to overshoot it.

You would also end up with excess fumaric acid in the product this way. This can fixed later by washing with ice cold acetone though, but lots of fumaric = lots of extra struggle.

I also had bad results with room temp. acetone. I had to chill both FASA and spice solution as otherwise some stuff stayed in acetone. This is harder to achieve when you want long stirring.

But there is only one way to know  Will you try it?