If it's a planar reconstruction, wouldn't you just use a typical panoramic stitcher such as Microsoft Research's Image Composite Editor to stitch the input photos together?
Naturally, that means that you'll have to be more careful with your image taking to get a clean stitch, than you would be for Photosynth to recognise how images fit together, but if you're mainly interested in loading it in other programs, then that seems to fit your needs better.
On the other hand, people have written tools (e.g. http://pspcexporter.codeplex.com/ ) to export Photosynth pointclouds, so they must have a decent understanding of Photosynth's coordinate system. You could simply get said persons to build a version that also exported the camera frusta positions, focal length, + angles as well as the points + you would be well on your way to being able to view the photos in relationship inside of a 3D modelling program.