I was going over it and here are some reasons they could pull off Darkseid in Smallville if they really wanted too. Now, Brainiac, in seasons 8 Legion episode, revealed the Anti-Life Equation and it was also mentioned in season 9 by Clark. If Brainiac has got the Anti-Life Equation stored in his data bank than I believe the other Brainiac that left with Kera could have also had it and went through a boomtube at the end of season 8. She ended up in the Phantom Zone and possibly Brainiac ended up on Apokolips with a part of the Anti-Life Equation to tempt Darkseid coming.
Now, Michael Ironside is the Father General of Lois and I think could end up being a prime character to be possessed by Darkseid because of his influence and power. He also did the voice of Darkseid in the animated series. I know, I know: Darkseid possessing someones body, yeah. Doomsday didn't have a human side either. Remember, Smallville likes to change the rules. I also believe the Martian Manhunter will play a big role with Darkseid, having met in the past. I believe this because the blood the Martian destroyed in ep 18 or 19, I think, of Smallville season 9 and having to lie to Clark. The Martian is afraid of Darkseid and knows that he is coming and the blood could have possibly been Darkseid's. If Intergang shows up, than you know it's not that far away and Darkseid could too. Just making some points here.