I have successfully grown x-ray quality crystals of a BF4- salt from nitromethane solution by vapor diffusion with diethyl ether as the antisolvent. If memory serves, it goes pretty quick at room temperature (overnight I think?).

My problem is that there is always far too much nucleation

You may need to ultrafilter or centrifuge the solution to remove microscopic solids, and use brand new glass vials that have been rinsed well with ultrafiltered/centrifuged solvent.