You might be best off just getting a clamp-on butt flap fender for the rear and admitting defeat up front.
Alternately, you could chop 8 inches or so off of the front fender so that instead of passing through the fork, it stops at the back of the fork. The spray out the front won't be so perfectly controlled, but it will keep most of the water off of your feet and legs. Is the clearance on the rear about the same as on the front, or is there more room to breathe back there?
I was going to suggest the same thing. Zip Ties are your best friend.
I just bought the Planet Bike full coverage fenders and I love them. They come with little bridges and other stuff that allows you to attach them with Zip Ties. They worked awesome yesterday. I had to travel on a muddy road that's all torn up, and they kept me totally dry.
Anyway, REI has the SKS fenders for $30ish (?) and they also have the Planet Bike ones. However I bought mine at the Hub like Joe did (Steef suggested that earlier, and you're giving $$$ to a cool local shop).