OK, I'm answering myself in case this is useful to someone else in the future.

This information applies ONLY if you plan on leaving the States by air or sea.

Crossing the Tijuana border is a piece of cake if you have a valid visa or your country of origin does not require one. You'll be most likely 20 seconds in the booth, and you are out. HOWEVER:

1.- Do not cross the San Diego border, use Otay instead (see below)
2.- MAKE SURE YOU CLOSE YOUR BIKE IN MEXICO ****BEFORE**** ATTEMPTING TO CROSS THE US BORDER. Ask the officers from customs in the Mexican side. DO NOT stand in line under any circumstances whatsoever before closing your bike in Mexico, as there is no such a thing as customs in the Mexican side crossing towards USA. The paperwork is done in a small building outside of the actual border IN OTAY. Ask for BANJERCITO in Otay. If you miss this point, you'll have to enter the US and then exit it again, and it will take you ages to do so, as you will probably go though US secondary inspection in order to go back to Mexico.
2.- You can jump in front of the line with your bike. Nobody will say a thing.
3.- The US officers in the OTAY side just want you to leave. I was missinfomed several times on the right procedure to cross with my bike, just beacuse they wanted to get rid of me. YOU MUST register your bike in the US IF you want to ship it back to your home country. Look for a big building next to a shopping center at the right of the border, as you enter the States. Officers in the OTAY border are absolute ignorants and only when I got to speak to the highest range officer on duty I could actually get a form stating that my bike had entered that day the country. This document is important because customs will need some proof of entry when you try to ship back your bike out of the country. If they refuse to give you any other entry document -such as a temporary import-, ask for the APPLICATION FOR EXPORTATION OF ARTICLES UNDER SPECIAL BOND and fill it out with your chassis number, license plate, and any piece of information that might be useful to identify your bike.
4.- Nobody cared about the EPA. But I'd do it just in case. It takes 10 minutes of your time to send an email.

There you go.