To cut a long story short, I ended up fixing this issue by myself and it wasn't too difficult as I have installed LEI before. The install hiccuped because it was looking for statements in the .profile of the notes account necessary for installing IEI. A sample of the statements in the .profile are provided below :

PATH=$PATH:/usr/bin:/etc:/usr/sbin:/usr/ucb:$HOME/bin:$HOME/lbin:/usr/bin/X11:/opt/ibm/domino/latest/ibmpow/res/C:/opt/ibm/domino/notes/latest/ibmpow:/local/notesdata:/sbin:.
export PATH;
LOTUS=/opt/ibm/domino;
export LOTUS;
LANG=C;
export LANG;
Notes_ExecDirectory=/opt/ibm/domino/notes/latest/ibmpow;
export Notes_ExecDirectory;
LIBPATH=$LIBPATH:$Notes_ExecDirectory;
export LIBPATH;
 

This is quite similar to the installation documentation for LEI 7.x, 8.x etc but in previous versions of the product, the .profile of the notes account did not have to be modified in advance to install the product successfully. Once the installation ran, it was pretty easy........

There was one interesting thing : the task is still loaded from the ServerTasks line in the notes.ini file, but the task is still called LEI (not IEI)  ! Oh well, I suspect  this will likely get fixed in the point release.