I ended up ordering an arbor spacer from Enco that looks like it should
do the trick. I looked around for a jam nut of the appropriate size but
I could not find any in the local hardware store and the places I saw
on the web wanted you to buy them in large (25+) quantity.

http://www.use-enco.com

In the mean time, i made my own spacer out of 1/2" MDF. It looks like
I'm still getting a little run-out with the MDF space but it wasn't bad
enough to stop me from turning a small bowl last night.

For folks' future reference: Be aware that if you purchase a Precision
Nova Midi Chuck by Teknatool, it may not fit on you lathe's spindle
without a little creative home engineering.