Maybe.... I have a plastic knob I scavenged off an old scrap piece of machinery I was thinking about trying to drill and tap. Not sure that the plastic would take any threads real well but figured, for free, I could give it a shot!
Alright, I got a "care package" from another member on here. It consisted of a few insert style boring bars and a handful of new inserts to go with. Really high end stuff and SUPER long life if treated properly. Anyway, the toolholder I had was a 3/8" square shank holder mainly made for hand ground tool steel and small size carbide holders.
I got down to work today and made a boring bar holder. Because there were two different size bars, I had to make a "double" holder.
Obviously I have to boring bars reversed for effect.... In operation there will only be one bar mounted and the mounted bar would be pointed towards the spindle