Give partial credit and having it show up on a results slide

You can't convert the score to text, but you could set up another question to calculate the score - so say using a pick one question with a set of offstage objects. You could set up some triggers and condtions to adjust which object is in a selected state based on the value of your variable (say select object 1 worth 10 points if the variable is greater than or equal to the total possible points for your drag and drop, select object 2 which is 8 points if the variable is less than 10 but greater than or equal to 8, and so on) as that question type allows you to set the score by choice and have a number of different options. It's a bit more complicated of a set up - but I think it would achieve the behavior you're describing.