The author of this patch is 'toby' from the MacPorts project, and the original commit containing this diff can be found at https://trac.macports.org/changeset/58563. The trac ticket prompting the commit (and with additional context) is at https://trac.macports.org/ticket/18357.
Toby, if you're reading this, apologies for not attributing the gist originally; I put this up quickly while experimenting with tmux under Leopard and abandoned it when it didn't solve the problem at hand. It's only fair now that other people are looking at the gist to give you credit.
Does this patch fix pasteboard interaction for you in Snow Leopard? It applies and compiles fine, and looks to be the appropriate change to make based on apple's patches to GNU Screen, but doesn't seem to have any effect for me.