In my experience - although my conditions are very different from yours - planting *anything*, but especially other solanaceae, near/under tomatoes is counter-productive: tomatoes are "all-around" consumers, so they'll deplete the soil's resources equally, but they are also "high" consumers, in that they deplete the soil quickly, plus they are somewhat picky about watering.
I'd say to leave the tomatoes alone, maybe try intermixing + surface fertilizer.

What to plant in this season: horseradish, perhaps? In my zone the roots are planted in October-November (full plant, of course, in spring).