Conflict in Eclipse Feature installation when one of the plugins already exists in the Eclipse instance

I have developed an Eclipse Feature Project, and I am using the open-source css validation plugin org.w3c.css in my feature. This plugin is also used by the Aptana Studio eclipse tool. If a user who has Aptana Studio installed in their Eclipse instance also wants to install my feature, a conflict results. Here's the jist:

Cannot complete the install because of a conflicting dependency.
...
    Only one of the following can be installed at once: 
        W3C CSS Validator 1.0.0.20110712 (org.w3c.css 1.0.0.20110712)
        CSS Validator 3.0.0.1303365277 (org.w3c.css 3.0.0.1303365277)

What I would like to have happen is the when my feature is being installed, 开发者_运维技巧if the org.w3c.css plugin is already installed, it doesn't break the installation. Ideally it would just pick the latest version and use that one, but any way that the installation can complete successfully would be great.

Here's the plugin declaration in my feature.xml, in case its of value:

   <plugin
         id="org.w3c.css"
         download-size="0"
         install-size="0"
         version="0.0.0"
         unpack="false"/>