I have previously described an idea that I call a "stepping stone bid." The name comes from the similar situation of throwing an opponent in to gain his card's value as an entry to Dummy (or hand) that you do not yourself have. Similarly (in a sense), a "stepping stone bid" is a call that does not take shape unless the opponent takes action, usually relying upon the need for the opponent to actually take action.
An example might be if you were to play that a 2C overcall of 1NT is a one-suited hand (Cappelletti, for example) but without any agreement that Advancer bids 2D to find out what you have. Instead, 2C just says you have a one-suited hand, and Advancer is free to pass. This would only make sense if we are white on red and limited severely as to strength. In that condition, the opponents cannot simply pass this out and defend a silly 2C contract, even if the score will be "down eight" for +400 to the opponents, because the opponents would be missing their vulonerable game bonus. Hence, 2C is not forcing on Advancer but rather conditionally forcing on the opponents.
A stepping stone bid, then, uses the condition of a force on the opponents as a means of having a "forcing" auction. This actually has some space-saving merit, in that this allows you two extra layers of description at a lower level. Consider the Cappelletti auction. If 2C is forcing on Advancer, the 2D relay means that we play 2D, 2H, 2S or 3C. If 2C is forcing on the opponents by the conditions that exist, however, we can bid 2C and play 2C, 2D, 2H, or 2S. Hence, you gain the ability to play one level lower in clubs when that is your suit. For that matter, you gain another step -- the redouble -- such that 2C could (in the situation of a conditional force on the opponents) safely show any one-suiter with the ability to play at the two-level and one additional meaning, perhaps weak with both majors or weak with both reds or something like that.
The point, though, is that a conditional force on the opponents is something we can in theory take advantage of in designing some isolated sequence options. As another example, consider a passed-hand Responder to a third-seat, whoite-on-red weak Two Hearts. You could decide that a 2S response is a weak escaqpe showing spades, clubs, diamonds, or both minors, non-forcing. If the opponents pass this out, they lose. So, they are conditionally forced to double. If they double, you can pass with spades, bid your minor with a one-suited minor, bid 2NT with both minors of equal length, or redouble with 6-4 in the minors (allowing Opener to bid a side 4-card minor or bid 2NT to ask for your minor).
Related to the Stepping Stone Bid is the "Bootstrap Bid." This is a call that boostraps onto the force actually created by the opponents. A simple example is a cuebid made by the opponents. If partner opens One Heart and RHO cuebids Two Hearts, this establishes a force on Advancer. Responder can use that force to facilitate more descriptive bidding himself, with free calls meaning one thing but passes-then-action another. There is nothing all that tricky about a Bootstrap Bid, but understanding the concept as such might create some interesting options that might not have been thought of before.
A third related concept is one I would call a Standoff Bid, which is related to the Boostrap Bid. A standoff is a situation where perhaps neither side likes the status quo. However, someone must blink. Because someone must blink, this requirement establishes a force itself. Moreover, one can use the forced blink as a defining tool, albeit with some risk of the Bluff Defense.
Let's consider an example. RHO opens a Multi 2D, guaranteeing a major. You play that a double shows "the other major." RHO cannot pass 2DX, so he must show his major. That, then, reveals your major to partner. Opener could use a "Bluff Defense" of bidding the major he does not have, of course, but that might get messy.
The point, though, is that the standoff creates an ability to stack meanings because the opponent not only must blink but in so doing must tell partner what you have. The standoff exists because in theory everyone could pass 2DX in the example. But, we expect them to blink first, so we send 2DX out there as a possible contract. I suppose that the other defense is the "All In Gamble," where 2DX is passed and played.