I have managed to solve my issue with yet another irksome workaround

, using the JUGA module and a bot snippet to call it from a static content item.
The instance of mod_hiddenbyjuga that loads in position "juga" contains another position, for instance jugagroup1, where a module of type Custom is loaded in turn. That custom module contains the info i want to show only to the group specified in mod_hiddenbyjuga.
All it takes is to replicate instances of the JUGA module for different access groups, instruct to load a different position in each instance and assign a custom module to that position. Notice that each instance of mod_hiddenbyjuga has also to load in a different position for each JUGA group, otherwise the snippet won't work.
Down to earth.
JUGA Group: G1
position for mod_hiddenbyjuga to load in: jugag1 (in this module you have to specify the JUGA group, of course; G1 in this case).
positition controlled by mod_hiddenbyjuga: jugagiload
position for the costum module: jugag1load
bot snippet to make this work:
It's not an elegant solution, but it works flawessly.
It would be slightly easier if JUGA coped well with the {modulebot} command.
Nuno.