In my case, the whole assembly fit in through one of the holes in the pumpkin.
I then fished the twist-ties out through the hole in the bottom to pull the board towards the hole. It took some dexterity to get the power supply plugged in, but then I just twisted the ties around a craft stick and secured everything with duct tape for extra security.
The first night the improved jack-o-lantern was outside it rained.
The base of the pumpkin filled with water, but the NeoPixels were still happily flickering away in the morning.
I cut some drainage holes and everything has been working great.