So is there a (simple) way to put a string into a scalar variable without any character escaping or processing of the contents of that string at all?

Not that I know of.

If you have large amounts of such data, maybe put them in a __DATA__ section, or into a config file.

That said, Perl 6 has a quoting construct Q'...' that doesn't have any escape sequences. Of course you can't escape the closing delimiter then.