97 Honda Civic DX hatch, rear speaker suggestions

I have a customer that has the 97 Honda Civic Hatchback.

If anyone has ever worked on one of these cars, you would know the rear speakers are mounted on plastic (6x9 din size).  My customer purchased a pair of cadence zx-691's from me to place in the rear deck.  The problem is that there is a large open cavity that goes over the wheel well that makes for a horrible "enclosure".  I offered to build custom boxes to fit inside the cavity to give better sound, but she didn't want to spend the cash to do that.  I was curious if anyone has some better, or more affordable solutions that I could offer to increase the sound quality that is lost in the rear of the car. 

Thanks

Craig

already looked into Q-forms and various other off brands, and noone makes an enclosure pre-fabbed for what I am looking for.