How to trigger hot plug detection in HDMI interface?
HDMI has a 5V line that can just be connected to the HPD line (a resistor is never a bad idea, just for short protection, 1k or so should do), but you also need to provide EDID (Serial EEPROM with appropriate contents) powered from the 5V line and connected to the I2C lines (I cannot off the top of my head remember if you need to supply the I2C pullup or if this is done on the card).

Further some HDMI parts sense the termination of the clock pair, so you would want to terminate this pair in a manner appropriate to the CML drive).