How about a research agreement where both parties agree the single tech to be researched at the start (i.e. it must be a tech neither has, but both can research)? Civ X contributes his whole beaker output, Bx. Civ Y also contributes his whole beaker output, By. Civ X pays Bygpt into the ether for the RA, civ Y pays Bxgpt. When they have, together, accumulated enough beakers, they both get the tech.
If the deal is interrupted (e.g. they go to war) before it is done, then both parties walk away with the total accumulated beakers, and each can continue researching it at his own pace.
That is something like what I envisaged when I first heard about RAs, in the pre-release hype.
It wouldn't necessarily work with tech costs as they are now, mind you; this suggestion is more expensive in terms of beakers per coin (at least from late medieval onwards) but allows more beakers to be bought in, if you've got the cash for it.