I looked at the suggestions here. I think the BOOT command would do what I need, but I don't know what I'm doing here.
As I gather it, I need a .img file of a working DOS boot disk. I can build the disk easily enough, but I don't know:
1) How to create the .img file. I've Googled and can't seem to find any Windows programs (I don't have a Linux box up at the moment) that I trust. I installed WinImage, but it doesn't have an option for .img and I don't know whether other formats work with DOSbox.
2) How to wrap the whole thing into a single command line so that the end user can just double-click an icon and use his software.