Categories with specified pullbacks

Dear all, I'm trying to track down a paper I once saw that I recall constructed, from a category with pullbacks, an equivalent category with *specified* pullbacks. I don't believe there was any strictness, in the sense that pulling back along fg was the same as the result of pulling back along one then the other. The feature I'm interested in is that I think that this construction required no global choice, except for one direction of the equivalence, which for me is no big deal. I may have misremembered this last bit, so I need to check the paper. Thanks, David -- David Roberts http://ncatlab.org/nlab/show/David+Roberts [For admin and other information see: http://www.mta.ca/~cat-dist/ ]