Whatever form that response takes it needs to be heavily derisive.
I think what Romney should say to all of the lies is:
“Look what he says when I am not around to correct him. Would he like to invite me to his next campaign speech?”
on the next debate he needs to bring this up to the empty chair , list all of what this idiot is saying and then go through them line by line and then finish off by saying” now I have given you the truth and I hope from here you will not go back and start saying I am lying as this is your chance to say anything right now and clear anything up”
“Romney should get a stock response together for these lies,”
Here it is:
“Mr. President, you are a liar. Now, prove me wrong.”
In the face-to-face context of the debates, I think a reprise of “There you go again!” would do nicely.
At the level of press releases, something along the lines of “President Obama has consistently shown that he believes his supporters’ inflated estimates of his oratorical ability, that partisan economic estimates are facts, and that policies that sound good in theory, but have never worked in practice will suddenly work when he tries them. It is hardly surprising that one who dwells in such a fantasy-land will claim that uncomfortable facts are ‘lies’.”
Romney should not just have responses at the ready, he needs to make pre-emptive strikes before Obama even has a chance to attack.