Is there a reason why you can't just remove them and have them cleaned at the drycleaners?

What I would do, as an alternative to having them dry cleaned, is simply remove them and wash them on the delicate cycle with a mild soap, put them in the dryer on "fluff," and then put them back on the cushions. A lot of things that say "dry clean only" can be handwashed or washed on "Delicate" in the machine. :)

Try this on an inconspicuous spot first. I cleaned several office chairs that I had purchased at auction, not knowing what kind of fabric or what cleaning was required. They came out spectacularly well.

* Combine 1/4 cup liquid dish detergent or laundry detergent and 1 cup warm water.
* With a hand mixer, whip until dry suds form (the suds will look like whipped cream).
* Test upholstery in an unnoticeable area by applying dry suds with a cloth or soft brush and lightly scrubbing.
* Allow to dry.
* If the area looks the same but cleaner, the entire piece of upholstery may be cleaned in this manner.
* Shampoo only a small area at a time and use a spatula or rubber scraper to lift off dirty suds.
* Repeat if necessary, then wipe area with a clean cloth dipped in clear water and wrung nearly dry.
* Dry completely.

I have two of the Lane outdoor wicker rockers on our screened porch. The cushions for them were very expensive when we purchased them in 2000. The fabric is supposedly not drycleanable or washable. We've kept them relatively clean, however, by keeping them under roof (porch or lanai) and by using a mixture of Dawn and water, with a bit of Lysol thrown in, too. First we vacuum the cushions with the upholstery brush. Then, spray the cushions all over with a light spray of 409 or Fantastic (extra on the spots). Then we dip a white terry washcloth into the cleaning bucket, wring it about half, and clean each side of the cushion. You may have to go over them two or three times if they are really dirty. We rinse the cloth in a separate bucket of clear water. If you do this about twice a year, your cushions will be clean without fading. You have to pay close attention to piping and the sides of box cushions, and we usually dry them in the sun. While they are drying we vacuum and clean the actual chair, so that the clean cushion goes back into a clean chair. If they are really dirty you can take them out in the yard and beat them until a lot of the dust is either out or brought to the surface, and then vaccum and clean. You can use a brush to get into the area around the piping, if that has been neglected for a long time.