You can use Apache Ivy to retrieve WordPress Plugins as dependencies by adding a URL Resolver to your ivysettings.xml file, as follows:

        <url name="wordpress-plugins">
          <artifact pattern="http://downloads.wordpress.org/plugin/[module].[revision].[ext]" />
        </url>

Then, within your ivy.xml file, you can add the plugins as dependencies, such as:

        <dependency org="com.contactform7" name="contact-form-7" rev="3.0.1">
            <artifact name="contact-form-7" type="zip"/>
        </dependency>
        <dependency org="com.wordpress" name="jetpack" rev="1.2.1">
            <artifact name="jetpack" type="zip"/>
        </dependency>
        <dependency org="com.wordpress" name="akismet" rev="2.5.3">
            <artifact name="akismet" type="zip"/>
        </dependency>
        <dependency org="com.janrain" name="rpx" rev="1.0.7">
            <artifact name="rpx" type="zip"/>
        </dependency>

The same approach can be used to treat any predictable download site as an Ivy Repository.