The speaker doesn't need to be very large. A light 8" would be just fine. Think bookshelf stereo speakers, then you're going the right direction.
When I've seen it done, the guy had the front head off. The speaker was suspended (cone facing the beater) and used rubber bands looped through the speaker mounting holes and the long end looped around the tuning keys.
I don't think you'll get a great sound out of it, but it may be usuable with a good para-eq. From what I remember there was more of a dirty thud than clean. But, I only heard it through a PA.