Using "unset zle_bracketed_paste" should do what you want, but I've only tried it in rxvt-unicode and the vte-based term I have. It stops zsh reacting to the escape sequences used by multi-line paste, see the docs for a full explanation¹.

If you were to use I'd recommend sticking it behind a "if $TERM" guard so that it you don't end up surprised if you switch to a term that doesn't warn at some point ;)

¹ http://zsh.sourceforge.net/Doc/Release/Parameters.html#index...