I don't see why they wouldn't have Vader in this. He was after the plans so maybe he could have something to do with them being stolen in the first place.
As previously posted, the force isn't a big part of ANH, and at this point Vader is just a general giving orders etc. They could still have Vader and not turn it into some twirly lightsaber fest. He could just be an all evil tyrant. Bring it.