Once again faced with exposure, Clark turns to Lois to write the story of "the Red-Blue Blur". It's a promising storyline, but you know the writers will backtrack from it some way, just as they've done multiple times with Lana.
What if Clark told Lois he was Superman and there were no take-backs? Lois and Clark explored this in the Season 3 premiere, when, after an ordeal, Clark proposes to Lois and she says, "Who's asking? Clark or Superman?"
Anyway, here's what I would say:
I know you must be mad. At me for not telling you sooner, at yourself for not seeing it, maybe not wanting to see it. We've been hiding from each other, haven't we? Me because I actually trusted you way sooner and way more than I thought possible. I wouldn't be telling you now, bringing the story to you, if I didn't.
You might look at me differently now, but you don't have to. I'm the guy who grew up in Smallville with Jonathan and Martha Kent. Clark Kent is who I always wanted to be, who I know I can be with you.
I'm not saying this would win Lois over. I'm single, after all. But it's how I would tell her.
UPDATE (9:14 PM): As we should expect from the super-oaf who is Smallville's Clark Kent, he didn't match wits well with the conniving Lake. After she turned the world against him, he decided to use the Legion's time travel ring to undo things.
Caroline Dries is one of the best writers of Lois and Clark dialogue, A shame in this case "it didn't really count." Smallville's draw has always been its different take on a classic mythos, but Clark too often seems far off the track to becoming the man he's supposed to be. At the same time the show never fully commits to its own direction. Clark can't be both indecisive and admirable, bashful and brave.