That should be Obama's selling point to the Blue Dogs. He should tell them the economy needs a bigger stimulus in order to show improved job numbers by the mid-term elections. And he should make sure they understand that they're more politically endangered next November if the the job numbers aren't moving in the right direction by then than if they vote for a larger stimulus now.
Democratic members of Congress have an irrational fear of the imagined "attack ad" which makes them frightened of actually supporting legislation for fear Republicans will make it sound bad. Who knows, maybe in normal times that fear is rational. But if unemployment is this high a year from now - and I think it likely will be (happy to be wrong!) absent additional help - all incumbents in swing districts will have a lot to fear.