I'd like to say that I managed to pull it off, but I suspect that was a lot of luck on my part. If you haven't already gotten the fish, I wouldn't. Go ahead and try for the fishless cycle. It's just better for the fish.
If you've already gotten the fish, a lot depends on how many fish you have and how messy they are, also how susceptible they are to toxins. Get a test kit and test your water. Do the 25% water changes, and if it spikes too high, do a higher percentage water change. Do not feed too much or too often. That should take care of it.