You can create xml-file that calls ir.module.module objects update_list function. Like this:

<openerp>
    <data>
        <function model="ir.module.module" name="update_list"/>
    </data>
</openerp>

Now if you add this xml-file to module data (like you would add any other view definition or other xml-files) that update_list function gets called every time you update this module. For example you added this to a new module named "your_custom_module_updater",  so now you can start odoo with:

./odoo.py -u your_custom_module_updater 

and that module list should update every time from now on. 

*note: you still need to manually update the list for your_custom_module_updater to install it :)