So, the HDMI and the GPIO are entirely unrelated. In a standard setup, the GPIO only controls the touch portion of the display, and is entirely optional. The HDMI controls the actual image on the actual LCD display itself. So, you can wire the HDMI without the GPIO at all anyway.
Now, if you are asking about how I directly wired the HDMI, I did the following. First, I removed both the LCD's and the PI's HDMI ports by using flush cutters to snip the mounting connectors, and then by heating up the tiny data pins so that the connector would release without damage to the board. Then, I used a wire diagram to wire up all of the HDMI pins on the PI to all of the HDMI pins on the display using some tiny magnet wire (32 guage). After that, I hot glued over the wires so that they wouldn't be prone to damage. Please note that this is very difficult and it is extremely easy to damage either board while doing this. Shorts between pins are also very easy to make, so you will need a magnification lens just to see if there are shorts or not. Now, even though there are 19 connections on an HDMI connector, not all 19 are needed. The shielding connections, the CEC, and the NC pin are all not required for the HDMI signal to work.
