Unfortunately, there aren't any shortcuts I can suggest here.
Removing the deck may sound like a bit of an effort, but it's pretty straight forward and I think it will save you a world of pain in the end.
As for trying to straighten the blade holder in place, well again, I believe the only way to do this properly is to remove it.
Then you can put it in a press and use a straight edge to make sure it is going to run true.
This is the way that I would do it. Hope it helps.
