What sort of material/substance do people recommend for creating fillets between a pattern and a base board.... That can be painted over.

Filleting wax is okay but doesn't like paint.. 

Ive tried filler but its pretty messy.

Is there anything that applies like say filleting wax and can be smoothed with filleting ball tool nicely.

I basically want to create a fillet between my pattern and a base board, run a nice fillet round the bottom edge. Then seal it, 2k paint it and take a mould from it.

Thanks
Josh