An extremely ugly workaround may be to create a custom command template and instead of doing a "show run" equivalent to get your config, tell it to do a 'show tech'. Yes, it's a TON of data but you might be able to get it to pipe to start where you want "| begin running-config" or something. Probably would also then not do a comparison and make sure it doesn't show up in any change reports.
I forget but do any of these device types have a "backup" command that rolls itself up into a file that could be ftp/scp'd off? You could write a couple of jobs to backup and then transfer the files. This prevents you from actually seeing the configuration inside of Config Manager, but it at least provides you with a backed up configuration.