Alright, I don't seem to have found any info on this, so I figured I'd post it to show anyone who might find the info interesting, and to get any feedback y'all might have.
I have recently given up on the 'Lee Breech Lock' system. I just have too many dies that are non-Lee (Lyman, RCBS, etc.), that already have some sort of locking ring on them, and don't want to buy Lee's quick change bushings for every non-Lee die I own (or my Lee dies that don't already have them).
The two Lee presses that I have are going to have one permanent bushing installed that doesn't get removed. That leaves me with a problem... The Lee dies that I have fit nicely in their box, but the rings (without the bushing) doesn't really provide a ring that will stay in place, and installing split ring locking nuts make them too large to fit into the box (some thinner, non-split lock rings with set screws that can damage the threads will fit into the box, but I don't care to use those).
Myself being cheap, and looking for the lowest cost solution, got the idea from a picture of some Liberty dies that had two nuts that were to be screwed against each other to lock the die in place. If you take two Lee nuts, and screw them together (one is 'upside down'), with the rubber o-rings touching each other, you can create a very study, inexpensive locking nut that will fit into the original box, with some of the Lee locking rings that you may already have on hand. The o-rings being pressed together tightens the nuts together quite nice and securely
The 'replacement' Lee lock rings are currently $1, and the rubber o-rings are .50¢, not including any shipping costs (on Lee Precision's website). For a Lee Deluxe 4 die pistol set, that would be about $6 (less shipping) to be able to continue to use the Lee 4 die box, as most other replacement die boxes only hold 3 dies.
I would be interested to hear what other people have done, especially with their Lee 4 die sets.
Please don't turn this into a Lee bashing thread. That is not what this post is about. I personally am plenty satisfied with my Lee products, and am glad that they are a sponsor of CastBoolits.com. If you can't stand Lee, that's fine, I just don't think this is the thread to express that.