The second-tier outfit visit the Allianz Arena to face the already-crowned Bundesliga champions and Pokal holders, with a berth in the tournament final up for grabs.
Bayern have eased off since winning their 24th German title in March, and successive league defeats to Augsburg and Borussia Dortmund will give Runjaic some confidence.
"We do not go to Munich to swap jerseys," Runjaic said.
"We are conscious of our inferiority, but that can also be liberating.
"I believe! But of course the faith is one thing, and the implementation on the pitch (is) the other."
Kaiserslautern defender Marc Torrejon, meanwhile, feels work-rate and sticking to Runjaic's game plan can help them claim a famous victory.
"We want to win, that's our goal, but it is very, very difficult. We need to work well and run a lot," Torrejon said.
"We need to (keep) Bayern, which is currently the best team in the world, doubled on the outside while keeping the centre tight.
"We also need to defend forward and take advantage of the few opportunities (we get)."
