Red Dot on S&W 52-2

[NUCWO3]

I'm trying to install an Aimtech APM-352 mount system on a S&W 52-2 so that I can mount a red dot sight. The "no gunsmithing" mount installation requires replacing 2 pins in the pistol frame with screws. The trigger pin pushed out easily enough, but the mainspring housing pin won't budge. I suppose that's because of the pressure of the mainspring. However, I don't see any way to relieve that pressure while driving the pin out.

Is there some technique I should know about that will allow me to remove the mainspring housing pin?

Thanks,
NUCWO3