I felt that I had to modify a ImageJ slightly. I believe that all of these changes will be part of future releases.
I added a scale plug-i for the FloatingProcessor class. I added an ImageJ constructor that accepts an applet reference. I store the applet reference in the Info class. Consequently, imageJ can acquire applet parameters and values. (I hear Wayne Rasband fixed that in the newest release of ImageJ).
I suggest future ImageJ versions should make the ij.properties file an applet parameter, so that any applet can have its individual list of plug-ins and the author of an applet can name the properties file.