You could just set the condensor for your largest format and leave it there. The purpose of the condensor is to distribute light evenly over the negative area. If it is even over a 6x7 area, it will be even over a 35mm, 6x4.5, and 6x6 area. The only real gain you get by matching the condensor precisely to the format is increasing light output for smaller formats, and that is usually small--typically on the order of 1/2 stop between medium format and 35mm--only really of interest if you are printing really big from 35mm.