The only real alternative for making enlargeable negatives with a pack-film camera is adapting an empty film pack to take a single 3x4 film sheet. As long as the camera has a film speed setting close to the speed of the actual film used, you should be able to dial in exposure with the lighten-darken dial. Major downside, though, is that this method doesn't support a dark slide, so it's a one-shot camera unless you carry a changing bag and feel like fiddling with this in the field (I've done it a couple times, when I wanted to test a Polaroid without committing a $10+ pack of film). You *could* preload multiple packs and store them in light-tight containers (old 4x5 film boxes, for instance), changing them in a changing bag -- but honestly, there are few Polaroids worth this kind of effort, and the few that are would (IMO) merit permanent conversion to 3x4 or 4x5 ANSI film holders (the latter of which would, if the conversion is made with this in mind, allow use of 405 or 545 backs to regain Polaroid functionality).