Just support them with a net made of criss crossing strings attached to sticks taped to the reservoir sides. As long as you are using a nutrient with adequate calcium they will stiffen up fairly quickly.
As long as adequate calcium is supplied a fan is not needed and is actually often detrimental as it can cause clogged stomas. Oscillating fans should really only be used in conjuction with a humidistat and should only blow directly on plants enough (very liitle) to prevent air stagnation that can cause problems associated with high humidities such as decreased transpiration, decreased respiration, mold, mildew, fungus etc. While lowering the humidity increases transpiration, directly blowly air is not a desireable way to dehumidify as it can easily clog stomas. It is better to just control the humidity with a dehumidifier and leave the stem strengthening to proper calcium uptake not the mythology of fan use.
Or take it from someone like Roseman who uses massive ventilation and fans pointed directly at his plants and then states all plants need high humidity and therefore humidifiers. Ventilation is fine to control excessive temps, just don't blow air directly on the plants unless it is a very gentle breeze, preferably an oscillating breeze. Some peope try to control humidity and temperture both with an exhaust fan but that seldm really works well as although realtive humidity is related to temperature you can have a wide range of relative humidity at the same temperature so one fan or one thermostat can not really control both and do it well.
