It should have been Lore, or nothing. Either Data decides to activate him to bring him back into the light, basically, or the Romulans steal him to lure the Enterprise/Data into a trap.
What exactly was the point of the scene where they find B4 and are chased? What would have happened to them had they been caught or killed? What was Shinzon's plan with that?
The Remans couldn't have used Lore for the trap because the ENT crew wouldn't have let their guards down for a moment-unless the Remans just totally reprogrammed Lore to be more like how B4 was. At any rate, the trap didn't work since the crew gave them deliberately inaccurate info.