You could use "holder" instead of "location":
now the initial position of x is the holder of x.
See ยง8.17. Looking at containment by hand.
But it will only include the object that is directly holding x, whether that is a container, supporter, or room. It'll be "box," for instance, not "the box in Room 101."
If you want to print the text of the holder and the location, and don't need the variable to be an object, you could do something like this:
When play begins:
repeat with x running through all things:
if the holder of x is a room:
now the start position of x is "[the location of x]";
otherwise:
now the start position of x is "[the holder of x] in [the location of x]".