Its fairly simple to multicast or dot the same spell almost instantly without hardware or software.
You use your keyboard hardware to set alt tab to work on just a single key press. We will call that key 1
On your main wow window, bind your spell to key 2
On your other wow windows, make a /assist macro /cast spell and have it assist your main window character and cast the spell, also bind to key 2.
So all you have to do is press 2 1 2 1 2 1 2 1 2 as fast as you can and you now have 5 corruptions on you. Remember to press 1 again to go back to main window.
You will also have to edit windows settings to progress yout alt tabs in order, and not prioritize your previous screen