Here's the relevant text, which precedes his now infamous September 9 "lipstick on a pig" comments:
"John McCain says he's about change too. Exce- and and so I guess his whole angle is watch out, George Bush, except for economic policy, healthcare policy, tax policy, education policy, foreign policy, and Karl-Rove-style politics, we're really gonna shake things up in Washington."
Here's the cartoon, which appeared in the September 5 Washington Post:
This lends credence to the belief, though it certainly does not establish it, that what appeared to be improvisation was deliberate.
(Update: From the Boston Globe)