How to force upgrade of optional

Hi,

Using Makefile.PL, I often feel a need to enforce the upgrade for
an optional module, but only when that module is already installed.

I have many modules which more or less depend on each other.  Sometimes,
my modules get interface improvements which are usable by other optionally
installed related modules.  I would like to be able to trigger an upgrade
of these optional modules, only when they are installed.

So, besides enforcing an upgrade to a minimal version
   PREREQ_PM => { XML::Compile::Tester => '0.05'}

an upgrade-if-installed to a minimal version
   UPGRADE_PM => { XML::Compile::Cache => '0.90' }

Or is there an other nice generic way to achieve this?
-- 
Regards,
               MarkOv

------------------------------------------------------------------------
       Mark Overmeer MSc                                MARKOV Solutions
       [email protected]                          [email protected]
http://Mark.Overmeer.net                   http://solutions.overmeer.net