That's correct...you can only do this kind of thing, using the Form_Current event, on a Single View Form. Doing it using the Form_Current event, on either Datasheet or Continuous View Forms, will set that Control on all Records to the Value that is appropriate for the Current Record.
To make the value of an Unbound Control appropriate to a given Record, on Datasheet or Continuous View Form, you have to use its Control Source Property. If you wanted the Unbound Control to display a sales tax of 5%, say, and the calculation was
ItemCost * 0.05
then in the Control Source Property you'd enter
=[ItemCost] * 0.05
If you're saying that you only want a Value to appear in that Unbound Control on the Current Record, but nothing to appear in thatControl on any other Record, I can't think of a way to do that, nor, to be honest, imagine why you'd need to.
What, exactly, do you want to display in this Control?