There was a beefed up unofficial version of AmigaGuide written that allowed inline pictures and other enhancements, while being totally compatible with existing .guides. I'm sure if you can find that it will have copy and paste. It's likely called something like 'MagicGuide' or Super whatever... you get the idea ;-)
Have a look on Aminet under /text/hyper.
Other than that, just open the guide in a text editor and search for the text you want :-)