Thanks for all the information above . I too had the case where my passport was renewed and hence was not issued I94 till my petition expiry in 2019 .  Based on all the guidance provided in various posts ,
I decided to give it a try today and I am back with new I94.

Below is my story and step by step process for you  Date of Travel 31 May 2017

1. I reached San Diego Airport around 9:30 AM .  As soon as you come out of the airport from the exit near the information booth , you can buy your day pass for 7$ from MTS kiosks .
   You will find the bus stop for 992 on the right side towards the San Diego downtown .

2. You will see the charts displaying the time of the bus arrival.

3. After Bus journey of about 5-10 Minutes, you can get down at Broadway/Kettner stop which is across America plaza Trolley station . (Starbucks is next to it, get your coffee if you can :))
   Within few steps you will see the  blue line trolley directions to San Ysidro.

4. Take the trolley and again get down at the last stop.

5. As soon as you get down , again in the direction of train , you will see the board where it is clearly mentioned the Pedestrian path to Mexico.

6. Before  starting for that direction , get yourself fresh in the restrooms in the McDonald compound.  There is paid restroom for 25 cent. Keep the change.

7. Once you are ready to go , follow the directions to Mexico . After 2-3 minutes of walking , you will find the first revolving door. Enter through that door and walk towards your right (left is already closed). Walk few steps and you will find the Mexico customs. You will get your 1 day Visa and move towards your right. Follow the path towards USA

8. You will reach USA , follow line for general public and Tell US officer you are here for I-94, They will check you visa and let you in after security without any incoming stamp as you need new I-94

9. Now you are back in  same trolley station from where you left. Now you need to go to I 94 permit office which is just opposite of Panda Express, please see below on google maps

    From  --> U.S. Customs and Border Protection - San Ysidro Port of Entry, 720 E San Ysidro Blvd, San Diego, CA 92173
    to    --> Panda Express, 4463 Camino De La Plaza #107, San Ysidro, CA 92173



10. Once you reach there you will see people waiting for I94 outside building exact opposite of Panda Express, wait in line for your turn which takes about 20/40 minutes.

11. Once you enter make payment for I94 and handover your passport/ I797 to officer. After verifying the  details , she provided me with new I94 till my petition expiry .

10. Come out of the building and then proceed towards trolley stop.

11. Again you can use the same day pass to take  blue line back to America Plaza and 992 to San Diego Airport.


Total time in mexico was just 20 minutes after my 1 day Mexico visa was approved, once you are back in US , I94 permit office is in USA only as per above map.