Don't you need a developed root system that's at the bottom of the pot for matting?
I have done my own tomatoes in a waterbath for sowing, after germination, then after transplanting into 3" pots and I've had no probs. I've been topping up the water every 4 days or so but the compost is still damp. I only put in about 1cm (when the pots are IN the tray) so you could put in 2 which should do 7 days. I wouldn't advise any deeper. The water is sucked up by the compost (not the roots) by capillary action, but the roots will grow long very quickly.
Mine haven't dampened off or anything, they're thriving.
However....this is not to say it will work for you........