Incomplete measure at end

Right click->Bar properties->Set the actual duration

That sounds like a feature that could be added to the New Score Wizard - on the New Score Wizard screen for Time Signature, Number of Measures, etc., right under the interface for designating the number of beats in the "Pick Up Measure" could be a similar interface for designating the number of beats in the final measure of the score.

But in the meanwhile, there is already a way to have an "incomplete measure at the end." Simply right click on the final measure. In the second section of the resulting pop-up dialog box, "Measure Duration," enter in the field beside "Actual:" the number of beats you want that measure to have. If you need something other than a whole number of beats, change the denominator as well, using the drop down menu beside the field; for example, if your score is in 4/4 time and you need 2 1/2 beats in the final measure, rather than typing "2" in the field, you would type "5" and then choose "/8" from the drop-down menu. Incidentally, if you need to insert an anacrusis in a score that you have already started, you can use the same procedure: insert the extra measures at the beginning, right click on the first one to make into the pick-up measure, and enter the number of anacrusis beats in the pop-up dialog.

Alternatively, you could just leave the final measure its normal length, with rests at the end marking the unused beats corresponding with the anacrusis - I have seen published music following this procedure as well.