hey lestweforget
its ONLY an idea, but the paintbrush bristles inspired me - so here goes : you could try using modelling clay, like milliput etc, to make a rough haystack shape, and whilte wet use your chopped up bristles and press them in randomly, lay them flat, poke them out etc, until the block is completely covered in bristles, spray paint it white once dry then base coat it brown, adding a darker, then lighter yellow as a maincoat and highlight, perhaps a final highlight with a cream color - use some twine/string for rope around them and bingo, one haystack!
hope thats clear (as mud) let me know if it helps, i might try it if it does lol
alpha :-)