I don't know too much about tomatoes, but chilli's have a similar taste (they like the same type of fertiliser), I use Potassium Nitrate / Salt Petre that's been used for making slow matches in solution as a fertiliser to be added to the chilli's water. Don't overdo it when adding solution to the water of the tomatoes.
Most of the guys on here will know how to make their own KNO3, but I don't think your neighbours would be overly happy about it.