Credit goes to Steam user "Press start to begin" for this solution.
Go to the level "The Lost City." Make your way through to the first bat section. Simply stand at one end and spin the bats. Every time a bat hits another, you'll get a single wumpa fruit, and with how closely packed the bats are, this can be 5-10 wumpa a cycle. Eventually, you'll get enough wumpa that you'll gain a life. Rinse and repeat until you hit 99 lives.