I have problems understanding your problem.

you said in the OP

> I don't want to have my scripts mention that someone else's __DATA__ is opened on some line urelated

• So either the warn is for an end-user, then hide all coordinates by appending "\n"
• Or it's for you, then ignore the DATA part.

This might be a little irritating, but IMHO it's a not too tragic side-effect of Perl trying to be explicit.