After using the search function, I have determined that there are no other threads about this "sling bow". The reason I bring it up is because BrianGrubbs showed me a link to this video:
http://www.youtube.com/watch?v=-6LxKfpAPYA&feature=channel_page (Thanks Brian!)
The video, of course, is all about how to construct what the man calls a "sling bow", a combination of a slingshot and a bow. I watched it, liked what I saw, and made my own. I used exactly the same model of slingshot and whisker biscuit, and the results were pretty good. (It almost seems like the parts were made for each other!)
While doing some archery earlier that day, I damaged the nock of one my arrows when my next arrow clipped it on its way into the target. This damaged arrow became my test arrow for the slingbow (as the nockless rear was easier to grip through the pouch). I was able to hit the shooting block (and get good arrow penetration) pretty consistently, but only after compensating for the arrow's tendency to go to the left.
To test what was causing this tendency, I held the slingshot vetically for a few shots, and found that it now shot low. I concluded that my arrow would stray in the direction of wrist brace. This could either be because of my improper form or due to the arrow.
Just as it's important to match a bow to the arrow, I suppose it may be important to match an arrow to your slingbow. For what it's worth, in the video he recommends carbon arrows, but I was using an aluminum arrow.
Also, as advertised, the whisker biscuit easily flips down and it can be used as a standard slingshot again at will.
Has anyone else attempted to make one of these? If so, what are your experiences with it?