I'd do twice daily 50% water changes to keep the levels as low as you can while the cycle rides out. You can also ease things a bit for the fish by adding some salt to the water, it helps counteract the physical effects nitrites have on fish.
In future, if you set up another tank and want to do a fishless cycle, you can do it with old fish food, or a decaying piece of fish or seafood (I recently read an article about cycling new marine tanks with raw prawns - gross, but effective!). It's not as precise as adding specific amounts of ammonia, but it does work - as a matter of fact, I just finished a fishless cycle using old nutrafin flake food