To get rid of floater shadows you can do like PolyHertz suggested, only with one change to make things easier. You hide or get rid of the rest of the mesh when you render the floaters. Makes combining them much more simple, provided nothing casts a shadow on your floaters...
Sa7an : not really anymore no :P Must faster with today's tools! As for the floaters I did not clean them on that example, but it is really fast to do. A matter of minutes most of the time.
is there a way to render ao without getting that annoying shadow around floaters? regarding the process: depending on the texture i sometimes use the highpass filter to push the contrast around edges. pior: do you still use this or a similar technique? http://www.pioroberson.com/tuts/tut_texturing_tricks.htm
Well if the floater ao is being a problem just render two maps, one with and one without them. Then you can use the 'clean' map as a wholy masked layer over the other in photoshop and just un-mask the areas you want to remove the shadows from on the 'dirty' map.
I find its easiest to render a skylight pass in Max - this gives you a decent AO pass (I use a mentalray AO as well) that doesn't give you shadows around your floaters as it uses a different calculation method for its shadows. Then I just mask between the two, using whichever gives me a better result.