While you have the sprite you want to drag and drop selected, go to where you can see the small picture of it, where you type in the sprites name. Then go right a bit and you will see a padlock. Unlock this by clicking on it and the sprite will be draggle online and in presentation mode.
Also you could use the following script:
<when green flag clicked>
<forever>
<if><<<touching [mousepointer]<and><mouse down?>>>
<repeat until><< <not><mouse down?>>>
<go to [mousepointer] >
<end>
<end>
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This project shows you how:
http://scratch.mit.edu/projects/keroro645/288561
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