Lopez, 39, was to marry Courtney Mazza, 31, Saturday in an event to be televised as a 2-hour special Dec. 8 on TLC.
Kardashian told People magazine she had a bit of advice for her co-host ahead of his big day.
"We talk during rehearsals and commercial breaks, and he's like, 'What time did you cut the cake?'" she said. "I'm like, 'I don't know. I was so wasted at my wedding.'
"You and your partner should take a few minutes to yourselves and just watch the whole thing from the audience," Kardashian said she suggested. "[My husband] Lamar and I will now talk about those little moments, because you get pulled away from each other. You shouldn't spend your whole wedding not with each other."
Lopez said he considers himself "just a sidekick" in Saturday's wedding.
"My fiancee is the star," he added.
"I just want the wedding itself to be fun, just a blast, everybody to party and have fun and to go all night."