opengl : a second rendering buffer ?

Is there a buffer in opengl that I could use as a "scrath render buffer" during the rendering process ? That is, drawing triangles in it, then recovering infos such as texture coordinates, and drawing other triangles into the true buffer with some perpixel treatment based upon infos read in the "scratch buffer". The reason I can''t use the main buffer as a scratch, then cleaning it and draw my final scene, is that I need two buffer to draw each triangle, and constantly need to go from one to the other. What I''m waiting from that buffer mainly is having UVW Texture coordinate availables for each pixel (and optionaly Depth) after a triangle has been drawed. Note that since the triangles I draw in the scratch buffer and in the real buffer are different, a fragment shader based solution only is not enough (though I''ll have to use it for the rest of my process).