Tools:
Drill with 1/4" drill bit
Electrical Tape (or tape of equal smoothness/thickness)
First, start with an unmodified RFR/DS shell:

Next, take the shell, turn it over and drill through the center of the hole in the bottom of the shell. Make sure to keep the drill bit straight as you go through. If you did it right, the entire post assembly inside the dart should simply fall out the front, leaving you with this (sorry for the blurry pic, but you get the idea)

Now, you should be left with a black circular piece of plastic inside the dart which is held up by a spring. This is part of the "air restrictor" assembly inside the dart, but since you just drilled out the center of it, you can simply leave it in the shell. I tried to remove it from the first shell and ended up botching it, destroying the shell. It's not hurting anything by being in there, so just leave it.
The next issue I ran into was that both the stock darts as well as Stefans/Streamlines would fall out of the shell, because the shell diameter was not tight enough against the dart to hold it in (that is what the post was for, apparently). So, to fix this, simply cut a small (~1/2") strip of electrical tape, and put it inside the shell just below the top opening. You should end up with something that looks like this:

Now, the darts should fit snugly in the shells without falling out. And...That's it! You're done. You should be able to use Stefans with the shells now. I also noticed a fairly significant increase in range due to drilling out the air restrictors, as well as slightly widening the hole in the back of the shells using the 1/4" drill bit.
IMPORTANT NOTE: One unfortunate issue is that normal-sized Streamlines will not work with the RFR, because they are just slightly too long to fit up into the breech cavity. You can either cut down your Streamlines by a small amount (I'm guessing somewhere between 1/4" and 1/2" would work), or, if you're like me and don't want to mutilate your darts, you can just use either the stock darts, or your own (shorter than Streamline) Stefan darts, which is what I chose to do. In the end it looks like this:

Hope this helps some people out with making these guns a little bit more useful. Questions or comments are welcome, though it's a fairly straightforward and simple procedure.








