I just uploaded version 0.10.0.
This version adds a simple "world clock" and an option for selecting the displayed time zone.
Also, this version hopefully fixes some issues which were mentioned here.

Fixed in 0.10.0.
Was reading an integer from gconf whereas it should have been float.

The complete source code can be found in the SVN repository at the garage site:
https://garage.maemo.org/projects/advclockplugin
Patches are also welcome (as long as they don't break any existing logic).
Or you could write your own addition as skykooler mentioned.
Advanced Clock Plugin is intended to be open for extension by others via custom "clock styles".

For this use case I'd suggest to add another "clock style".
A good start would probably be to copy the existing DecimalClock.
Of course you would need some String input field in the configuration plugin and a method for adding that string to the clocks.
I could add a free text field and set it in a way such that the text is available when inheriting from the Clock base class.
This would others also to use that free text probably for even completely different purposes.

Currently, all options that can be set via the options frontend are accessible when inheriting from the Clock base class.
So anyone writing a custom clock can access these fields.
Have a look in clock.py to see what is currently available.