I'm not sure it's possible with Explorer HAT Pro. The LCD needs 6 pins, and Explorer HAT Pro only exposes 5 ( BCM 8, 9, 10 and 11 and 18 which are CS, MISO, MOSI, SCLK and PWM respectively ).
If you were to move the Explorer HAT Pro off your Pi, you could use the other CS pin ( CE1 ) to gain the 6 connections you need- using BCM 7, 8, 9, 10, 11 and 18- none of which are used by devices on the Explorer HAT Pro.
An LCD with an I2C Backpack would be much easier- since it only requires SDA, SCL, 3v3 and GND.
You can't use any of Explorer HAT's outputs to interface an LCD either- since these sink to ground ( when you turn them on they make a connection to ground ) and will, at best, invert your logic making it useless ( unless you modify the library ) and, at worst, damage something which isn't 5v tolerant.
At a stretch, you might be able to use Output 1, for example, for Pin 4 of the LCD, the Register Select pin, if you either modified the Python library to invert the logic, or used a transistor, and put a suitable voltage divider circuit on your breadboard it might well be possible.
The easiest thing to do is take your Explorer HAT Pro off your Pi- whether you use a Black HAT Hack3r for this, or a handful of jump wires and a breadboard is up to you, but it'll make your life easier for getting this up and running.
In the mean time, I'll either attempt this myself, or find out of it's practical to write up a tutorial- since this isn't an entirely terrible idea!