*Nothing* formats CD-RW or DVD-RW discs so they can be used like floppies. This is because RW discs use a complex system of light-sensitive dyes to operate, and can only be erased and re-written about 200 times before they start to fail. They can't be randomly accessed, because this would require erasing and re-writing information in the file table for every single file written to the disc - the disc would be kaput before you even finished filling it up. Even if they could, the process would be slow and unreliable. RW discs are not the same as floppies.
I suggest having a good look at "Burn Folders" in Mac OS X, as that might be closer to what you want. USB memory keys might also be more convenient for your needs.