um, well, if you don't mind making changes to the shipped slick C code you might be able to do it like this. The lines of code below can be found in the workspace_new_project2 function in the project.e source file. The first line was added by me. It adds the gp123.txt file to the project just before the project properties dialog appears. It's not a very nice way to do it though.
project_add_file('c:/gp/gp123.txt'); // <<<<<<<<<<<<<< added
if (ShowPropertiesDialog) {
result=show('-modal -mdi -xy _project_form',new_project_name,_ProjectHandle(new_project_name),PROJECTPROPERTIES_TABINDEX_FILES);
//toolbarUpdateFilterList(new_project_name);
}
Another possibility is to create a new project but with no files in it. Then open the project.vpj file in a text editor and scroll down to the "Files" xml node near the end. You could write some software to add whatever source files you wanted to the project xml file and use it as the start of a new project file - or if you don't want to modify the xml, make the workspace and the project active and call the project_add_file function (like I do above) to add whatever files you want.
So you could create a new dialog using the slick C form designer with an edit box on it for someone to enter the project name, you then make a copy of the project xml file template, give it a new name, create a workspace xml file as well, make it active, then call project_add_file repeatedly to add whatever files you want, then call the project_edit command to open the project properties dialog. You can probably use the copy_file function to create any files you need.