Whoa!!!! I'm a sewing nut. Stitch Witchery and Steam a seam are designed to be permanent. These are not temporary solutions. Of the 2, the Steam a seam 2 is the easier product to use as you can temporarily adhere it with the pressure of a finger. As soon as you touch it with a hot iron, it is semi-permanent. By that, I mean that it is intended to be permanent, but I've had some come apart after years of use.
All said, it's not a bad way to do a hem on a fabric that can tolerate a hot iron...but it won't work if you are looking for a "do it yourself" that you plan to have re-done later.
For a temporary job, there is a sewing product called ResQ tape. You could also use double sided scotch tape. Either of these could be removed and properly hemmed when you get home.