It is a bit manual.. but no other way at the mo..
Create a new file with an .inc extension, place one letter/character in it - then save it (move it) in the Include folder that the IDE uses (ie: ../Masm/Include)
Then add it in with the project explorer window that's on the RHS of the IDE .. (R-click -> Add Include Files).
You could create the file with wordpad (etc..) and save it with an .inc extension in the include folder.
Create it as a module within Easycode, save it, then change the extension to .inc and move it to the include folder, then add it in the Project Explorer.
Maybe Ramon might build in a facility for this in the later versions.