Acraglas and nothing else.
First of all don't dremel. The right way to do a grip reduction is by heat, then very lightly sanding out the rough spots. If you do it right, then there won't be much sanding. I would also recommend sanding off the finger grooves at this point, as well as undercutting the trigger guard if you want to (it makes a big difference). If you do the grip reduction by sanding alone, you will sand away the backstrap, leaving only the resin showing, which cannot be stippled. It will also be much weaker in the end.
What you do is get a heat gun and heat up the backstrap. Wearing gloves, roll the protrusion of the grip on a flat metal surface, like the tang of a vice. Once it's flat enough for you, sand the edges to blend them into the frame. The finished product should be a straight line, like on a 1911.
At this point, I like to take the wood burner and fill in the hole for the retention lanyard. You take one of the backstraps that came with the pistol, cut it into little pieces, then use the spade shaped bit from the wood burner to melt them into place, plugging that hole.
Next you drill a hole in the inside of the frame, so that the resin has a mechanical lock. Then go into the backstrap with a small rasp or pointed file and rough up the interior as much as possible.
Then fill with Acraglas from Brownell's. This is important because Acraglas is the only thing that will flex. That void in the backstrap acts as a recoil dampener, so you want something that can absorb that shock. Marine tex is too stiff and brittle. I've seen many examples of Marine tex cracking and falling off due to the recoil induced flex of the polymer frame. After the Acraglas is set up, I would give it two days, sand off the excess. You can bevel it or leave it flat. Personally, I like a bobtail cut because it prints less under a shirt.
I found out that this is how the custom shops do it, at least the ones doing it right. So that's their big secret. Heat instead of sand, and use Acraglas instead of Marine tex or JB Weld. Some claim to use some special filler in the Acraglas, but I don't see it as being necessary. It's plenty strong, and you need flexibility more than added strength.
Whatever you do, do not use a soldering iron to stipple. It will come out horrible. You need a variable temp wood burner with a needle point bit and a spade bit. When you go to do the stippling, start by flattening the existing texture with the spade bit, then sand it smooth. This way, you're not sanding away material. After you have a smooth surface, mark out the areas you want textured in masking tape, and stipple a border. I highly recommend staying away from the web and trigger guard areas. To do the actual stippling, use the needle point at high temp. It should make a sizzling sound immediately and put off smoke. You need that bubbling effect to raise the most texture from the least amount of polymer. It should only take a split second of contact to raise one stipple, and not require much pressure. If you do indexes for the trigger fingers, or texture high up on the grip, remember that those areas house the rails that the slide rides on. They're embedded into the polymer, and if you weaken those areas you could cause problems. It's a good idea to move around a lot, too, as the heat builds up fast. Work on one area for a minute, then move to another area to let that one cool down.
You'll want to wear a full respirator the entire time. The Acraglas puts off fumes while it's curing, the dust from sanding it is probably very unhealthy (nowhere in its original purpose was sanding involved), and the fumes from the stippling will give you quite the headache if you're not wearing a good respirator.
Remember two things. It's worth it, and Glock will send you a new frame for 100 bucks if you mess it up. So you have much to gain and very little to lose.
ETA: For your first time, it might be best to stipple before adding the Acraglas. That way if you get carried away and heat up the backstrap too much, you won't ruin the bond between the Acraglas and the frame.
