I've never seen or even heard of one of these attachments. Do you have a picture or model # of one in particular? Found a video here what may be of some help, tho that guy is using regular sand instead of baking soda. Using regular sand when (dry) bead blasting is usually a big no-no, but perhaps it's less of an issue when it's watered down.
I was a little surprised to see the venturi on that contraption able to **** up dry media like that, but it did appear to work. As expected, the spray nozzle didn't seem to last all that long for the guy, but that might be less of an issue if you're using soda.