With this, although the store at Ultimarc indicates that it is out of stock:
http://www.ultimarc.com/optipac1.html
Then you just need to install a serial mouse driver for DOS (and have a computer with a serial port, of course). I've never tried to get any USB stuff working with the PC in mine, so I don't know if that is possible, and there may be other options, but this is the one I've used and it works very well.