I just tried this on mine, and learned a few things, so here's a how-to:
First unscrew the T5 set screw from the inner side near the temple. Be very careful not to drop it.
Slide the lens out from the temple side first, and look for the washer. The washer is a rubber piece that the set screw goes into. It sort of makes up for the lack of 'hook' that the R2 lens lacks, but HJ ones do. Here's a comparison picture.
Since X-metal doesn't bend like O Matter, the washer keeps the small notch in place.
Once you remove the lens, you can insert the HJ lens, nose bridge side first, and simply slide the rest into place. There may be a gap as some have said, but you just need to puch a little further. They won't stay as is, but I looked through the set screw hole, and if I could push it just a little further, the screw would fit. I really thing you may need to grind the notch down maybe half the width of the screw hole (not much), rather than grinding anything else.
I don't have any spare lenses, but I have the display rack, which is just as well for this experiment, since it says the color in huge letters. Enjoy.
For the Asian exclusive look:
For evening
I'm sorry I said such bad things about you fire...
For nighttime
For class
For Ali G yo
For evening, but pretending it's daytime.