I just brought a kindle touch that arrived on Friday. I only really read in the bath so did a lot of reading up on which kindle would be best for this. This thread came up in my google searching along with others and videos. I ended up borrowing a friends and having a go with a freezer bag solution for water protection. I was convinced that i could make the touch controls work.
Having finally gotten my kindle, and my own waterproof case similar to the one shown in this thread I had great success making the case work well with the touch, without any attachments needed to be added to the kindle. I made a quick video showing the technique, so feel free to have a look here
http://youtu.be/3a7VwzeqewoThe gist of it though is all you need to do is keep the bag really open as you seal it to trap some air in the case... once some air is trapped this stops the cover from touching the screen and making the touch inputs not work well, or at all.
I've read with this method for the first time last night, and whilst it was a bit iffy right at the corners of the screen (the moisture from the finger print annoyed me so i was trying to make it not be over the text of the book) it works perfectly fine.
It's even easier to do it with a ziplock freezer bag as their plastics are much lighter. The protection is probably much less though than the cover i have, or the trendy one already shown in this thread.
Have no fear though, you definitely can use the touch like this, and its absolutely fine!!
Happy reading!