lost keys, push button start?

Hmmm... if you lost the keys, the presumably you lost the keyfobs as well?  How did you get into your car if you lost your keys and keyfobs?

Your SE may have an engine immobilizer, which requires the actual key (transponder chip is embedded in the plastic of the actual Nissan key).  If that's the case, you need to get your car towed to Nissan, and have them outfit your vehicle with a new set of keys and a new immobilizer chipset (may also be done via Nissan programming).

and you cannot just buy an immobilizer bypass unit, b/c you'll need an actual key to program the bypass unit.

To be quite honest, I have no idea how you'll bypass the immobilizer without having Nissan re-program or re-issue (keys).  This is MORE than a locksmith just cutting you new keys -- it's a computer chip that emits a radio signal and it's embedded in the head of the factory nissan key.  This radio signal communicates with a receiver around the key cylinder on the steering column and de-activates those starter interupts you've read about.

You can disconnect the positive terminal of the battery (at least) to deactivate the factory alarm.  Leave it disconnected for at least 10 minutes

well your factory arm and disarm are through your lock and unlock. Why dont you try to pulse your unlock wire to shut off the alarm. But that doesnt solve your case for driving the car. Theres no way possible for you to drive it unless you have a transponder. Which you dont. do yeah. your screwed dude. call a locksmith is your only chance. NOTE if you break the sterring lock. it will cost you more money in the future to fix. I KNOW!