I have just updated the initial post, with a link to v. 1.07, which includes:
1) now the user can also select the insertion point of the ex libris in the TOC;
2) added --no-guide switch to prevent inserting the ex libris in the guide;
3) added --guide-string and --toc-string switches to specify the strings to be used for the ex libris in the guide and in the TOC lists.
IMPORTANT: the option switch -i, which was used to specify the insertion point of the ex libris in the spine, has been renamed to -s (spine) to be consistent with -t (TOC) switch.