Thanks for all the help from everyone! I will outline my steps below so that if anyone is doing this with a window manager not found in the repo, they will have the steps to do so...
1. After compiling your desired window manager you will need to create a small script to load it during the boot process under $PACKAGE_DIR/usr/local/tce.installed/newwm. It can be something as simple as:
#!/bin/sh
echo newwm > /etc/sysconfig/desktop
2. If the new window manager requires command line parameters to be passed, you will need to make several more adjustments before packaging. If it doesn't, then you can skip to the last step.
3. Rename the window manager to have a proceeding dot (e.g. cd $PACKAGE_DIR/usr/local/bin; mv newwm .newwm)
4. Create another shell script in the appropriate bin directory (e.g. $PACKAGE_DIR/usr/local/bin/newwm) that will call the renamed binary from the proceeding step with all the parameters that need to be passed:
#!/bin/sh
exec /usr/local/bin/.newwm -xyz -123 ...
5. Now package your window manager, place it in the 'optional' directory, adjust the onboot.lst file (or whichever lst file you are booting with), and reboot!
NOTE: be sure to "chmod 755" both of those shell scripts before packaging!
Dave