You know those fake flowers and plants in the craft stores? Would those be fish safe? I recently got a bunch from my aunt and I can't think of another use for them.
I have 2 in my 20 gallon female tank. 1 silk, and the other is plastic. I washed them off really good, with the hottest water I could stand. The stems are plastic covered wire. I bent the stems into a circle to use as a base, then covered it with gravel. The girls love them. They sleep in/on them at night.
I wouldn't put them in - just because of the glues they use to glue them together, along with the wire inside the stem - that will rust and start to degrade, and also the coloring they use on the actual flowers could come off in the water.
I use plastic plants that I purchase from craft stores. I silicone the holes that can be seen near the wire part. I've never had a problem.
I don't have any experience with dyed floral plastic/silk plants though. Perhaps soak them for a few days,changing the water out a couple of times a day.