No, we don't have the entity resolver local entity set externalized such that it could be expanded. Create an RFE on sourceforge and we can look into adding this.
I had the same problem and finally found a solution that worked for me.
In the DOCTYPE declaration for struts-config (etc) you will see the reference to the DTD used to validate the XML file. Usually something like this:
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.2//EN" "http://jakarta.apache.org/struts/dtds/struts-config_1_2.dtd">
Given this is struts, I am assuming this is for a webapp so create a directory under WEB-INF called "dtds" or something. Then get this actual dtd from the struts distributable or from the URL in the doctype declaration and put it in your local dtds directory.
Then change the DOCTYPE declaration to:
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.2//EN" "dtds/struts-config_1_2.dtd">
This tells the XML validator to look in the local (relative) path for the DTD. This assumes your struts-config.xml is in the WEB-INF root.
Hope it works for you