Older IDE drives have a 40-pin connection (39 pins an one blank). These drives can be installed in parallel using a cable with two connectors. Just be sure that your current hard drive, the one with your OS and everything, is on the end of the cable rather than the middle and that it's set to be the master rather than the slave. Read more about master and slave settings
As for hot glue... I can't say that it's a bad idea. But I can't say that it's a good one, either. If you can add mount points by drilling the case, I'd do that instead.