If you turn the light on quite a bit, try moving your water bowl under the light. The light will help to evaporate the water from the bowl, leading to more humidity in the tank.

You could also try giving your BP a humid hide. I have read others use this with some success. Take a tupperware type container and cut an opening large enough for your BP to enter by. Put some damp moss in there and when your BP needs a little more humidity they can just go in there. But I think those that use one could help you out with this better.

If you do go with the floral foam, i would change it maybe at least once a week. I would worry too, that with leaving the same peice in there too long bacteria would build up on it.