There is a post-instantiation mechanism: define a proc package_name_post_instantiation and it will be called everytime you create a new instance of the package from the site-map. For an example look at file_storage_post_instantiation.
You are looking for something else obviously, just though I'd mention that anyway.
I don't see a problem with creating a group-type in plsql though, the tcl proc doesn't do more than call the corresponding plsql function either. What else do you need to do on installation?
