The Queen guitarist explained that he has been working with the production team for a while to create a certain kind of image of the late frontman.
May told BBC News that the "effect" will not be a hologram, and described it as "an optical illusion of sorts", in a similar vein to the recent resurrection of Tupac Shakur at the Coachella Festival.
"People will come out saying, 'Did we actually see Freddie?" he said.
"It's a little unfortunate they did that thing with Tupac as we've been trying to make Freddie appear on the stage for quite a while.
"[That technique] is something we've looked at ourselves but I think probably for a show that runs eight shows a week it's not really quite practical."
The special edition of the musical will be staged at London's Dominion Theatre on May 14 to celebrate 10 years on the West End.
Producer Robert De Niro will also be making an appearance on the night, May confirmed.
"There is a certain person who's coming that's intimately associated with getting the production on in the first place - our friend Bob from Los Angeles," May said.
"We call him Bob so we don't get too overcome with his stardom."
Queen's Roger Taylor recently stated that he did not oppose a Freddie Mercury hologram, but insisted he would never perform live with one.
Watch the video for Queen's 'We Will Rock You' below: