After walking away last night angry and disgusted about the state of vnc4 support in Ubuntu, it occurred to me that I could the regular Debian version of the package.
I obtained the Debian source package for vnc4 for lenny from: http://packages.debian.org/source/lenny/vnc4
I then manually patched unix/xc/programs/Xserver/vnc/vncExtInit.cc. (I moved the include of XserverDesktop.h to immediately after the include of stdio.h.)
Finally, I built the package in the usual manner: debuild -us uc
There are only two binary packages built from the Debian version of vnc4: vnc4server and xvnc4viewer. I uninstalled the Ubuntu vnc4server and vnc4-common binary packages (using apt-get purge), and then used dpkg to install the binary packages that I had just built.
I am happy to report that everything appears to be working fine. The vnc4config tool no longer crashes on startup, and I can now happily cut-and-paste from my vnc session.